A318560 - OEIS

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A318560

Number of combinatory separations of a multiset whose multiplicities are the prime indices of n in weakly decreasing order.

1, 1, 2, 2, 3, 4, 5, 3, 8, 7, 7, 8, 11, 12, 15, 5, 15, 17, 22, 14, 27, 19, 30, 13, 27, 30, 33, 26, 42, 37, 56, 7, 44, 45, 51, 34, 77, 67, 72, 25

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OFFSET

1,3

COMMENTS

A multiset is normal if it spans an initial interval of positive integers. The type of a multiset is the unique normal multiset that has the same sequence of multiplicities when its entries are taken in increasing order. For example the type of 335556 is 112223. A (headless) combinatory separation of a multiset m is a multiset of normal multisets {t_1,...,t_k} such that there exist multisets {s_1,...,s_k} with multiset union m and such that s_i has type t_i for each i = 1...k.

The prime indices of n are the n-th row of A296150.

LINKS

Table of n, a(n) for n=1..40.

EXAMPLE

The a(18) = 17 combinatory separations of {1,1,2,2,3}:

{11223}

{1,1122} {1,1123} {1,1223} {11,112} {12,112} {12,122} {12,123}

{1,1,112} {1,1,122} {1,1,123} {1,11,11} {1,11,12} {1,12,12}

{1,1,1,11} {1,1,1,12}

{1,1,1,1,1}

MATHEMATICA

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