OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..500
FORMULA
Weigh transform of A032153.
EXAMPLE
The a(5) = 7 compositions:
(5) = (5)
(41) = (4)*(1)
(14) = (14)
(32) = (3)*(2)
(23) = (23)
(131) = (13)*(1)
(212) = (2)*(12)
Not included:
(311) = (3)*(1)*(1)
(113) = (113)
(221) = (2)*(2)*(1)
(122) = (122)
(2111) = (2)*(1)*(1)*(1)
(1211) = (12)*(1)*(1)
(1121) = (112)*(1)
(1112) = (1112)
(11111) = (1)*(1)*(1)*(1)*(1)
MATHEMATICA
nn=50;
ser=Product[(1+x^n)^Total[(Length[#]-1)!&/@Select[IntegerPartitions[n], UnsameQ@@#&]], {n, nn}];
Table[SeriesCoefficient[ser, {x, 0, n}], {n, nn}]
PROG
(PARI) WeighT(v)={Vec(exp(x*Ser(dirmul(v, vector(#v, n, (-1)^(n-1)/n))))-1, -#v)}
seq(N)={WeighT(Vec(sum(n=1, N-1, (n-1)!*x^(n*(n+1)/2)/prod(k=1, n, 1-x^k + O(x^N)))))} \\ Andrew Howroyd, Dec 01 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 31 2018
STATUS
approved