A333328 - OEIS

A333328

Irregular triangle read by rows: T(n,0) = A002182(n) and T(n,k + 1) = A000005(T(n,k)), terminating at the first number which is not highly composite, n > 2.

4, 3, 6, 4, 3, 12, 6, 4, 3, 24, 8, 36, 9, 48, 10, 60, 12, 6, 4, 3, 120, 16, 180, 18, 240, 20, 360, 24, 8, 720, 30, 840, 32, 1260, 36, 9, 1680, 40, 2520, 48, 10, 5040, 60, 12, 6, 4, 3, 7560, 64, 10080, 72, 15120, 80, 20160, 84, 25200, 90, 27720, 96, 45360, 100

(list; graph; refs; listen; history; text; internal format)

OFFSET

3,1

COMMENTS

There are two questions related to this array: First, which rows have length greater than any previous row? Second, are there any rows which terminate at a k greater than 6?

LINKS

Table of n, a(n) for n=3..63.

James Grime and Brady Haran, 5040 and other Anti-Prime Numbers, Numberphile video (2016).

FORMULA

T(n,0) = A002182(n), T(n,k) = A000005(T(n,k - 1)).

EXAMPLE

The irregular triangle T(n,k) starts:

n\k 0 1 2 3 4 ...

3: 4 3

4: 6 4 3

5: 12 6 4 3

6: 24 8

7: 36 9

8: 48 10

9: 60 12 6 4 3

10: 120 16

11: 180 18

12: 240 20

13: 360 24 8

...

PROG

(PARI) A333328_rows(n)={my(N=Map(Mat([1, 1; 2, 2; m=4, 3])), p=2, F=[]); while(#N<n, if(numdiv(m)>p, mapput(N, m, p=numdiv(m)); my(M=List([m, q=p])); while(mapisdefined(N, q, &q), listput(M, q)); print(#N", "Vec(M)); F=concat(F, Vec(M))); my(s=if(m>=720720, 360360, m>=5040, 2520, m>=840, 420, m>=60, 60, 2)); until(numdiv(m+=s)>p, )); F}

CROSSREFS

Cf. A000005, A002182, A002183, A189394.

Sequence in context: A045814 A064218 A228780 * A109339 A071989 A290278

Adjacent sequences: A333325 A333326 A333327 * A333329 A333330 A333331

KEYWORD

nonn,tabf

AUTHOR

Davis Smith, Mar 15 2020

STATUS

approved