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A308296
a(n) = (1/n!) * Sum_{i_1=1..n} Sum_{i_2=1..n} ... Sum_{i_n=1..n} multinomial(i_1+i_2+...+i_n; i_1, i_2, ... , i_n).
4
1, 1, 7, 842, 7958726, 15467641899285, 10893033763705794846727, 4247805448772073978048752721163278, 1299618941291522676629215597535104557826094801396, 419715170056359079715862408734598208208707081189266290220651371206
OFFSET
0,3
LINKS
FORMULA
a(n) = A144510(n,n).
EXAMPLE
a(2) = (1/2) * (binomial(1+1,1) + binomial(1+2,2) + binomial(2+1,1) + binomial(2+2,2)) = 7.
PROG
(PARI) {a(n) = sum(i=n, n^2, i!*polcoef(sum(j=1, n, x^j/j!)^n, i))/n!}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 19 2019
STATUS
approved