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A331477
Number of n element multisets of n element multisets of an n-set.
2
1, 1, 6, 220, 73815, 286243776, 13949678575756, 8800321588119330984, 73241437035618231162682185, 8183604949527627465377060678018870, 12477686558866630120430437118910496237274716, 263383624455446425760290611316122951917033704595478840
OFFSET
0,3
LINKS
FORMULA
a(n) = binomial(binomial(2*n - 1, n) + n - 1, n).
EXAMPLE
The a(2) = 6 multisets are:
{{1,1}, {1,1}},
{{1,1}, {1,2}},
{{1,1}, {2,2}},
{{1,2}, {1,2}},
{{1,2}, {2,2}},
{{2,2}, {2,2}}.
MATHEMATICA
Table[Binomial[Binomial[2n-1, n]+n-1, n], {n, 0, 20}] (* Harvey P. Dale, Aug 19 2021 *)
PROG
(PARI) a(n)={binomial(binomial(2*n - 1, n) + n - 1, n)}
CROSSREFS
Main diagonal of A331436.
Sequence in context: A041623 A292692 A015477 * A144658 A203637 A144045
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Jan 17 2020
STATUS
approved