Displaying 1-10 of 12 results found.
Number of factorizations of n for some n (image of A001055).
+10
33
1, 2, 3, 4, 5, 7, 9, 11, 12, 15, 16, 19, 21, 22, 26, 29, 30, 31, 36, 38, 42, 45, 47, 52, 56, 57, 64, 66, 67, 74, 77, 92, 97, 98, 101, 105, 109, 118, 135, 137, 139, 141, 162, 165, 171, 176, 181, 189, 195, 198, 203, 212, 231, 249, 250, 254, 257, 267, 269, 272, 289
FORMULA
The Luca et al. paper shows that the number of terms with a(n) <= x is x^{ O( log log log x / log log x )}. - N. J. A. Sloane, Jun 12 2009
MATHEMATICA
terms = 61; m0 = 10^5; dm = 10^4;
f[1, _] = 1; f[n_, k_] := f[n, k] = Sum[f[n/d, d], {d, Select[Divisors[n], 1 < # <= k &]}];
Clear[seq]; seq[m_] := seq[m] = Sort[Tally[Table[f[n, n], {n, 1, m}]][[All, 1]]][[1 ;; terms]]; seq[m = m0]; seq[m += dm]; While[Print[m]; seq[m] != seq[m - dm], m += dm];
CROSSREFS
Factorizations are A001055 with image this sequence and complement A330976. The least number with exactly a(n) factorizations is A045783(n). The least number with exactly n factorizations is A330973(n). Cf. A002033, A007716, A033833, A318284, A325238, A330935, A330936, A330977, A330989, A330991, A330992, A330997.
Least value with A045782(n) factorizations.
+10
28
1, 4, 8, 12, 16, 24, 36, 60, 48, 128, 72, 96, 120, 256, 180, 144, 192, 216, 420, 240, 1024, 384, 288, 360, 2048, 432, 480, 900, 768, 840, 576, 1260, 864, 720, 8192, 960, 1080, 1152, 4620, 1800, 3072, 1680, 1728, 1920, 1440, 32768, 2304, 2592, 6144
EXAMPLE
Factorizations of n = 1, 4, 8, 12, 16, 24, 36, 60, 48:
{} 4 8 12 16 24 36 60 48
2*2 2*4 2*6 2*8 3*8 4*9 2*30 6*8
2*2*2 3*4 4*4 4*6 6*6 3*20 2*24
2*2*3 2*2*4 2*12 2*18 4*15 3*16
2*2*2*2 2*2*6 3*12 5*12 4*12
2*3*4 2*2*9 6*10 2*3*8
2*2*2*3 2*3*6 2*5*6 2*4*6
3*3*4 3*4*5 3*4*4
2*2*3*3 2*2*15 2*2*12
2*3*10 2*2*2*6
2*2*3*5 2*2*3*4
2*2*2*2*3
(End)
CROSSREFS
Includes all highly factorable numbers A033833. The least number with exactly n factorizations is A330973(n).
Numbers that are not the number of factorizations into factors > 1 of any positive integer.
+10
23
6, 8, 10, 13, 14, 17, 18, 20, 23, 24, 25, 27, 28, 32, 33, 34, 35, 37, 39, 40, 41, 43, 44, 46, 48, 49, 50, 51, 53, 54, 55, 58, 59, 60, 61, 62, 63, 65, 68, 69, 70, 71, 72, 73, 75, 76, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 93, 94, 95, 96, 99
COMMENTS
Warning: I have only confirmed the first eight terms. The rest are derived from A045782. - Gus Wiseman, Jan 07 2020
MATHEMATICA
nn=15;
fam[n_]:=fam[n]=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[fam[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
nds=Length/@Array[fam[#]&, 2^nn];
Complement[Range[nn], nds]
CROSSREFS
The least number with n factorizations is A330973(n).
Number of factorizations of n into distinct factors for some n (image of A045778).
+10
19
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 18, 19, 21, 22, 25, 27, 31, 32, 33, 34, 38, 40, 42, 43, 44, 46, 52, 54, 55, 56, 57, 59, 61, 64, 67, 70, 74, 76, 80, 83, 88, 89, 91, 93, 100, 104, 110, 111, 112, 116, 117, 120, 122, 123, 132, 137, 140, 141, 142, 143, 148
CROSSREFS
The least number with n strict factorizations is A330974(n).
Least value with A045779(n) factorizations into distinct factors.
+10
15
1, 6, 12, 64, 24, 256, 48, 512, 60, 96, 2048, 144, 210, 120, 216, 180, 384, 288, 16384, 240, 432, 420, 65536, 1536, 360, 480, 900, 864, 3072, 1152, 1296, 2310, 524288, 6144, 960, 720, 840, 2304, 1728, 1080, 1260, 2592, 2097152, 1800, 4608, 24576
EXAMPLE
The strict factorizations of a(n) for n = 1..9:
() (6) (12) (64) (24) (256) (48) (512) (60)
(2*3) (2*6) (2*32) (3*8) (4*64) (6*8) (8*64) (2*30)
(3*4) (4*16) (4*6) (8*32) (2*24) (16*32) (3*20)
(2*4*8) (2*12) (2*128) (3*16) (2*256) (4*15)
(2*3*4) (2*4*32) (4*12) (4*128) (5*12)
(2*8*16) (2*3*8) (2*4*64) (6*10)
(2*4*6) (2*8*32) (2*5*6)
(4*8*16) (3*4*5)
(2*3*10)
(End)
CROSSREFS
The least number with exactly n strict factorizations is A330974(n).
Least positive integer with n factorizations into distinct factors > 1, and 0 if no such number exists.
+10
14
1, 6, 12, 64, 24, 256, 48, 512, 60, 96, 0, 2048, 0, 144, 210, 120, 216, 180, 384, 0, 288, 16384, 0, 0, 240, 0, 432, 0, 0, 0, 420, 65536, 1536, 360, 0, 0, 0, 480, 0, 900, 0, 864, 3072, 1152, 0, 1296, 0, 0, 0, 0, 0, 2310, 0, 524288, 6144, 960, 720, 0, 840, 0, 2304
MATHEMATICA
nn=10;
fam[n_]:=fam[n]=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[fam[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
nds=Length/@Array[Select[fam[#], UnsameQ@@#&]&, 2^nn];
Table[If[#=={}, 0, #[[1, 1]]]&[Position[nds, i]], {i, nn}]
CROSSREFS
All nonzero terms belong to A025487. The version with zeros removed is A045780.
Sorted list containing the least number with each possible nonzero number of factorizations into distinct factors > 1.
+10
13
1, 6, 12, 24, 48, 60, 64, 96, 120, 144, 180, 210, 216, 240, 256, 288, 360, 384, 420, 432, 480, 512, 720, 840, 864, 900, 960, 1080, 1152, 1260, 1296, 1440, 1536, 1680, 1728, 1800, 2048, 2160, 2304, 2310, 2520, 2592, 2880, 3072, 3360, 3456, 3600, 3840, 4320
EXAMPLE
The strict factorizations of a(n) for n = 1..9.
{} 6 12 24 48 60 64 96 120
2*3 2*6 3*8 6*8 2*30 2*32 2*48 2*60
3*4 4*6 2*24 3*20 4*16 3*32 3*40
2*12 3*16 4*15 2*4*8 4*24 4*30
2*3*4 4*12 5*12 6*16 5*24
2*3*8 6*10 8*12 6*20
2*4*6 2*5*6 2*6*8 8*15
3*4*5 3*4*8 10*12
2*3*10 2*3*16 3*5*8
2*4*12 4*5*6
2*3*20
2*4*15
2*5*12
2*6*10
3*4*10
2*3*4*5
MATHEMATICA
nn=1000;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
nds=Length/@Array[strfacs, nn];
Table[Position[nds, i][[1, 1]], {i, First/@Gather[nds]}]
CROSSREFS
The least number with n strict factorizations is A330974.
Least number with each record number of factorizations into distinct factors > 1.
+10
7
1, 6, 12, 24, 48, 60, 96, 120, 180, 240, 360, 480, 720, 840, 1080, 1260, 1440, 1680, 2160, 2520, 3360, 4320, 5040, 7560, 8640, 10080, 15120, 20160, 25200, 30240, 40320, 45360, 50400, 55440, 60480, 75600, 90720, 100800, 110880, 120960, 151200, 181440, 221760
COMMENTS
First differs from A330997 in lacking 64.
EXAMPLE
Strict factorizations of the initial terms:
() (6) (12) (24) (48) (60) (96) (120)
(2*3) (2*6) (3*8) (6*8) (2*30) (2*48) (2*60)
(3*4) (4*6) (2*24) (3*20) (3*32) (3*40)
(2*12) (3*16) (4*15) (4*24) (4*30)
(2*3*4) (4*12) (5*12) (6*16) (5*24)
(2*3*8) (6*10) (8*12) (6*20)
(2*4*6) (2*5*6) (2*6*8) (8*15)
(3*4*5) (3*4*8) (10*12)
(2*3*10) (2*3*16) (3*5*8)
(2*4*12) (4*5*6)
(2*3*20)
(2*4*15)
(2*5*12)
(2*6*10)
(3*4*10)
(2*3*4*5)
MATHEMATICA
nn=1000;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
qv=Table[Length[strfacs[n]], {n, nn}];
Table[Position[qv, i][[1, 1]], {i, Union[qv//.{foe___, x_, y_, afe___}/; x>y:>{foe, x, afe}]}]
CROSSREFS
This is the strict version of highly factorable numbers A033833. The least number with n strict factorizations is A330974(n).
Record numbers of factorizations into distinct factors > 1.
+10
6
1, 2, 3, 5, 7, 9, 10, 16, 18, 25, 34, 38, 57, 59, 67, 70, 91, 100, 117, 141, 161, 193, 253, 296, 306, 426, 552, 685, 692, 960, 1060, 1067, 1216, 1220, 1589, 1591, 1912, 2029, 2157, 2524, 2886, 3249, 3616, 3875, 4953, 5147, 5285, 5810, 6023, 6112, 6623, 8129
EXAMPLE
Representatives for the initial records and their strict factorizations:
() (6) (12) (24) (48) (60) (96) (120)
(2*3) (2*6) (3*8) (6*8) (2*30) (2*48) (2*60)
(3*4) (4*6) (2*24) (3*20) (3*32) (3*40)
(2*12) (3*16) (4*15) (4*24) (4*30)
(2*3*4) (4*12) (5*12) (6*16) (5*24)
(2*3*8) (6*10) (8*12) (6*20)
(2*4*6) (2*5*6) (2*6*8) (8*15)
(3*4*5) (3*4*8) (10*12)
(2*3*10) (2*3*16) (3*5*8)
(2*4*12) (4*5*6)
(2*3*20)
(2*4*15)
(2*5*12)
(2*6*10)
(3*4*10)
(2*3*4*5)
MATHEMATICA
nn=1000;
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
qv=Table[Length[strfacs[n]], {n, nn}];
Union[qv//.{foe___, x_, y_, afe___}/; x>y:>{foe, x, afe}]
PROG
(Python)
def fact(num):
....ret = []
....temp = num
....div = 2
....while temp > 1:
........while temp % div == 0:
............ret.append(div)
............temp //= div
........div += 1
....return ret
def all_partitions(lst):
....if lst:
........x = lst[0]
........for partition in all_partitions(lst[1:]):
............yield [x] + partition
............for i, _ in enumerate(partition):
................partition[i] *= x
................yield partition
................partition[i] //= x
....else:
........yield []
best = 0
terms = [0]
q = 2
while len(terms) < 100:
....total_set = set()
....factors = fact(q)
....total_set = set(tuple(sorted(x)) for x in all_partitions(factors) if len(x) == len(set(x)))
....if len(total_set) > best:
........best = len(total_set)
........terms.append(best)
........print(q, best)
....q += 2#only check evens
print(terms)
CROSSREFS
The least number with n strict factorizations is A330974(n).
Numbers k such that the number of factorizations of k into distinct factors > 1 is a prime number.
+10
5
6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 62, 63, 65, 66, 68, 69, 70, 74, 75, 76, 77, 78, 80, 81, 82, 85, 86, 87, 88, 91, 92, 93, 94, 95, 98, 99, 100, 102
COMMENTS
First differs from A080257 in lacking 60.
EXAMPLE
Strict factorizations of selected terms:
(6) (12) (24) (48) (216)
(2*3) (2*6) (3*8) (6*8) (3*72)
(3*4) (4*6) (2*24) (4*54)
(2*12) (3*16) (6*36)
(2*3*4) (4*12) (8*27)
(2*3*8) (9*24)
(2*4*6) (12*18)
(2*108)
(3*8*9)
(4*6*9)
(2*3*36)
(2*4*27)
(2*6*18)
(2*9*12)
(3*4*18)
(3*6*12)
(2*3*4*9)
MATHEMATICA
strfacs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[strfacs[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
Select[Range[100], PrimeQ[Length[strfacs[#]]]&]
CROSSREFS
The version for strict integer partitions is A035359. The version for integer partitions is A046063. The version for set partitions is A051130. Numbers whose number of strict factorizations is odd are A331230. Numbers whose number of strict factorizations is even are A331231. The least number with n strict factorizations is A330974(n). Cf. A001318, A045780, A318286, A328966, A330992, A330993, A330997, A331023/ A331024, A331050, A331051, A331200, A331232.
Search completed in 0.009 seconds
| 