A381452 Number of multisets that can be obtained by partitioning the prime indices of n into a set of multisets and taking their sums.

1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 2, 2, 1, 3, 1, 3, 2, 2, 1, 4, 1, 2, 2, 3, 1, 5, 1, 3, 2, 2, 2, 4, 1, 2, 2, 5, 1, 5, 1, 3, 3, 2, 1, 5, 1, 3, 2, 3, 1, 5, 2, 5, 2, 2, 1, 7, 1, 2, 3, 4, 2, 5, 1, 3, 2, 5, 1, 6, 1, 2, 3, 3, 2, 5, 1, 6, 2, 2, 1, 8, 2, 2, 2

Offset

1,6

Comments

First differs from A045778 at a(24) = 4, A045778(24) = 5.

Also the number of multisets that can be obtained by taking the sums of prime indices of each factor in a factorization of n into distinct factors > 1.

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.

A multiset partition can be regarded as an arrow in the poset of integer partitions. For example, we have {{1},{1,2},{1,3},{1,2,3}}: {1,1,1,1,2,2,3,3} -> {1,3,4,6}, or (33221111) -> (6431) (depending on notation).

Sets of multisets are generally not transitive. For example, we have arrows: {{1},{2},{1,2}}: {1,1,2,2} -> {1,2,3} and {{1,2},{3}}: {1,2,3} -> {3,3}, but there is no set of multisets {1,1,2,2} -> {3,3}.

Links

Robert Price, Table of n, a(n) for n = 1..1000

Formula

a(A002110(n)) = A066723(n).

Example

The prime indices of 24 are {1,1,1,2}, with 5 partitions into a set of multisets:
  {{1,1,1,2}}
  {{1},{1,1,2}}
  {{2},{1,1,1}}
  {{1,1},{1,2}}
  {{1},{2},{1,1}}
with block-sums: {5}, {1,4}, {2,3}, {2,3}, {1,2,2}, of which 4 are distinct, so a(24) = 4.

Mathematica

prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]& /@ sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}];
mps[mset_]:=Union[Sort[Sort/@(#/.x_Integer:>mset[[x]])]&/@sps[Range[Length[mset]]]];
Table[Length[Union[Sort[Total/@#]&/@Select[mps[prix[n]], UnsameQ@@#&]]], {n, 100}]

Crossrefs

Before taking sums we had A045778.

If each block is a set we have A381441, before sums A050326.

For distinct block-sums instead of blocks we have A381637, before sums A321469.

Other multiset partitions of prime indices:

- For multisets of constant multisets (A000688) see A381455 (upper), A381453 (lower).

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

- For set multipartitions (A050320) see A381078 (upper), A381454 (lower).

- For sets of constant multisets (A050361) see A381715.

- For set systems with distinct sums (A381633) see A381634, zeros A293243.

- For sets of constant multisets with distinct sums (A381635) see A381716, A381636.

More on sets of multisets: A261049, A317776, A317775, A296118, A318286.

A000041 counts integer partitions, strict A000009.

A000040 lists the primes.

A003963 gives product of prime indices.

A055396 gives least prime index, greatest A061395.

A056239 adds up prime indices, row sums of A112798.

A122111 represents conjugation in terms of Heinz numbers.

A265947 counts refinement-ordered pairs of integer partitions.

Cf. A000720, A001222, A001970, A002846, A066328, A213385, A213427, A299200, A299202, A300385, A317142.

Sequence in context: A345345 A056924 A342083 * A316364 A318357 A323091

Adjacent sequences: A381449 A381450 A381451 * A381453 A381454 A381455

Keyword

nonn

Author

Gus Wiseman, Mar 06 2025

Status

approved