OFFSET
0,3
COMMENTS
Also the number of composable pairs of integer partitions of n, where a partition is regarded as an arrow from (number of parts) to (number of distinct parts). Is there a nice choice of a composition operation making this into an associative category?
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..1000
FORMULA
EXAMPLE
The a(0) = 1 through a(5) = 10 pairs:
()() (1)(1) (2)(2) (3)(3) (4)(4) (5)(5)
(11)(2) (21)(21) (31)(31) (41)(41)
(111)(3) (31)(22) (41)(32)
(22)(4) (32)(41)
(211)(31) (32)(32)
(211)(22) (311)(41)
(1111)(4) (311)(32)
(221)(41)
(221)(32)
(2111)(41)
(2111)(32)
(11111)(5)
MATHEMATICA
Table[Length[Select[Tuples[IntegerPartitions[n], 2], Length[Union[#[[1]]]]==Length[#[[2]]]&]], {n, 0, 15}]
PROG
P(n, y) = {1/prod(k=1, n, 1 - y*x^k + O(x*x^n))}
R(n, y) = {prod(k=1, n, 1 + y/(1 - x^k) - y + O(x*x^n))}
seq(n) = {my(g=Vec(P(n, y)), h=Vec(R(n, y))); vector(n+1, i, my(p=g[i], q=h[i]); sum(j=0, poldegree(q), polcoef(p, j)*polcoef(q, j)))} \\ Andrew Howroyd, Dec 31 2022
CROSSREFS
The inhomogeneous version with containment and multiplicity is A339006.
The inhomogeneous version with containment is A355383.
The inhomogeneous version with containment for compositions is A355384.
The version for compositions is A355388.
A001970 counts multiset partitions of partitions.
A063834 counts partitions of each part of a partition.
A323583 counts splittings of partitions.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jul 02 2022
EXTENSIONS
Terms a(26) and beyond from Andrew Howroyd, Dec 31 2022
STATUS
approved