A381636 - OEIS

A381636

Numbers whose prime indices cannot be partitioned into constant blocks with distinct sums.

12, 60, 63, 84, 120, 126, 132, 156, 204, 228, 252, 276, 300, 315, 325, 348, 372, 420, 444, 492, 504, 516, 560, 564, 588, 630, 636, 650, 660, 693, 708, 720, 732, 780, 804, 819, 840, 852, 876, 924, 931, 948, 975, 996, 1008, 1020, 1068, 1071, 1092, 1140, 1164

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OFFSET

1,1

COMMENTS

A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.

Also numbers that cannot be written as a product of prime powers > 1 with distinct sums of prime indices (A056239).

Contains no squarefree numbers.

Conjecture: These are the zeros of A382876.

LINKS

Robert Price, Table of n, a(n) for n = 1..1331

EXAMPLE

The prime indices of 300 are {1,1,2,3,3}, with partitions into constant blocks:

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

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

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

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

but none of these has distinct block-sums, so 300 is in the sequence.

The terms together with their prime indices begin:

12: {1,1,2}

60: {1,1,2,3}

63: {2,2,4}

84: {1,1,2,4}

120: {1,1,1,2,3}

126: {1,2,2,4}

132: {1,1,2,5}

156: {1,1,2,6}

204: {1,1,2,7}

228: {1,1,2,8}

252: {1,1,2,2,4}

276: {1,1,2,9}

300: {1,1,2,3,3}

MATHEMATICA

hwt[n_]:=Total[Cases[FactorInteger[n], {p_, k_}:>PrimePi[p]*k]];

pfacs[n_]:=If[n<=1, {{}}, Join@@Table[(Prepend[#, d]&)/@Select[pfacs[n/d], Min@@#>=d&], {d, Select[Rest[Divisors[n]], PrimePowerQ]}]];

Select[Range[100], Select[pfacs[#], UnsameQ@@hwt/@#&]=={}&]

CROSSREFS

More on multiset partitions into constant blocks: A006171, A279784, A295935.

These are the positions of 0 in A381635, after taking block-sums A381716.

Partitions of this type are counted by A381717.

For strict instead of constant blocks we have A381806, zeros of A381633.

For equal instead of distinct block-sums we have A381871.

A000688 counts multiset partitions into constant, see A381455 (upper), A381453 (lower).

A001055 counts multiset partitions, see A317141 (upper), A300383 (lower).

A050361 counts multiset partitions into distinct constant blocks, after sums A381715.

A055396 gives least prime index, greatest A061395.

A056239 adds up prime indices, row sums of A112798.

Cf. A000720, A001222, A005117, A050320, A059404, A213242, A293243, A299202, A300385, A381078, A381454, A381634.

Sequence in context: A099321 A097302 A075367 * A359419 A372135 A012658

Adjacent sequences: A381633 A381634 A381635 * A381637 A381638 A381639

KEYWORD

nonn

AUTHOR

Gus Wiseman, Mar 10 2025

STATUS

approved