A339658 - OEIS

A339658

Heinz numbers of loop-graphical partitions (of even numbers).

1, 3, 4, 9, 10, 12, 16, 25, 27, 28, 30, 36, 40, 48, 63, 64, 70, 75, 81, 84, 88, 90, 100, 108, 112, 120, 144, 147, 160, 175, 189, 192, 196, 198, 208, 210, 220, 225, 243, 250, 252, 256, 264, 270, 280, 300, 324, 336, 343, 352, 360, 400, 432, 441, 448, 462, 468, 480

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OFFSET

1,2

COMMENTS

Equals the image of A181819 applied to the set of terms of A320912.

The Heinz number of a partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k). This gives a bijective correspondence between positive integers and integer partitions.

A partition is loop-graphical if it comprises the multiset of vertex-degrees of some graph with loops, where a loop is an edge with two equal vertices. Loop-graphical partitions are counted by A339656.

The following are equivalent characteristics for any positive integer n:

(1) the prime factors of n can be partitioned into distinct pairs;

(2) n can be factored into distinct semiprimes;

(3) the prime signature of n is loop-graphical.

LINKS

Table of n, a(n) for n=1..58.

Eric Weisstein's World of Mathematics, Graphical partition.

FORMULA

A300061 = A339657 \/ A339658.

EXAMPLE

The sequence of terms > 1 together with their prime indices begins:

3: {2} 70: {1,3,4} 192: {1,1,1,1,1,1,2}

4: {1,1} 75: {2,3,3} 196: {1,1,4,4}

9: {2,2} 81: {2,2,2,2} 198: {1,2,2,5}

10: {1,3} 84: {1,1,2,4} 208: {1,1,1,1,6}

12: {1,1,2} 88: {1,1,1,5} 210: {1,2,3,4}

16: {1,1,1,1} 90: {1,2,2,3} 220: {1,1,3,5}

25: {3,3} 100: {1,1,3,3} 225: {2,2,3,3}

27: {2,2,2} 108: {1,1,2,2,2} 243: {2,2,2,2,2}

28: {1,1,4} 112: {1,1,1,1,4} 250: {1,3,3,3}

30: {1,2,3} 120: {1,1,1,2,3} 252: {1,1,2,2,4}

36: {1,1,2,2} 144: {1,1,1,1,2,2} 256: {1,1,1,1,1,1,1,1}

40: {1,1,1,3} 147: {2,4,4} 264: {1,1,1,2,5}

48: {1,1,1,1,2} 160: {1,1,1,1,1,3} 270: {1,2,2,2,3}

63: {2,2,4} 175: {3,3,4} 280: {1,1,1,3,4}

64: {1,1,1,1,1,1} 189: {2,2,2,4} 300: {1,1,2,3,3}

For example, the four loop-graphs with degrees y = (3,1,1,1) are:

{{1,1},{1,2},{3,4}}

{{1,1},{1,3},{2,4}}

{{1,1},{1,4},{2,3}}

{{1,2},{1,3},{1,4}},

so the Heinz number 40 is in the sequence. On the other hand, the three loop-multigraphs with degrees y = (4,4) are

{{1,1},{1,1},{2,2},{2,2}}

{{1,1},{1,2},{1,2},{2,2}}

{{1,2},{1,2},{1,2},{1,2}},

but none of these is a loop-graph, so the Heinz number 49 is not in the sequence.

MATHEMATICA

spsbin[{}]:={{}}; spsbin[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@spsbin[Complement[set, s]]]/@Cases[Subsets[set], {i, _}];

mpsbin[set_]:=Union[Sort[Sort/@(#/.x_Integer:>set[[x]])]&/@spsbin[Range[Length[set]]]];

nrmptn[n_]:=Join@@MapIndexed[Table[#2[[1]], {#1}]&, If[n==1, {}, Flatten[Cases[FactorInteger[n]//Reverse, {p_, k_}:>Table[PrimePi[p], {k}]]]]];

Select[Range[25], Select[mpsbin[nrmptn[#]], UnsameQ@@#&]!={}&]

CROSSREFS

A320912 has these prime shadows (see A181819).

A339656 counts these partitions.

A339657 ranks the complement, counted by A339655.

A001358 lists semiprimes, with squarefree case A006881.

A101048 counts partitions into semiprimes.

A320655 counts factorizations into semiprimes.

The following count vertex-degree partitions and give their Heinz numbers:

- A058696 counts partitions of 2n (A300061).

- A209816 counts multigraphical partitions (A320924).

- A000569 counts graphical partitions (A320922).

The following count partitions of even length and give their Heinz numbers:

- A027187 has no additional conditions (A028260).

- A338914 can be partitioned into strict pairs (A320911).

- A338916 can be partitioned into distinct pairs (A320912).

- A339560 can be partitioned into distinct strict pairs (A339561).

Cf. A001055, A001221, A001222, A007717, A056239, A112798, A320732, A320892, A338898, A338912, A338913, A339112.

Sequence in context: A325196 A242661 A336226 * A344297 A344292 A356823

Adjacent sequences: A339655 A339656 A339657 * A339659 A339660 A339661

KEYWORD

nonn

AUTHOR

Gus Wiseman, Dec 18 2020

STATUS

approved