OFFSET
0,4
LINKS
Robert Israel, Table of n, a(n) for n = 0..448
Eric Weisstein's World of Mathematics, Pochhammer Symbol.
FORMULA
Let w = exp(2*Pi*i/3) and set F(x) = (exp(x) + w*exp(w*x) + w^2*exp(w^2*x))/3 = x^2/2! + x^5/5! + x^8/8! + ... . Then the e.g.f. for the sequence is F(-log(1-x)).
a(n) = ( (1)_n + w * (w)_n + w^2 * (w^2)_n )/3, where (x)_n is the Pochhammer symbol.
MAPLE
f:= proc(n) local k; add(abs(Stirling1(n, 3*k+2)), k=0..(n-2)/3) end proc:
map(f, [$0..30]); # Robert Israel, Feb 12 2024
MATHEMATICA
Table[Sum[Abs[StirlingS1[n, 3k+2]], {k, 0, Floor[(n-2)/3]}], {n, 0, 30}] (* Harvey P. Dale, Jan 12 2024 *)
PROG
(PARI) a(n) = sum(k=0, (n-2)\3, abs(stirling(n, 3*k+2, 1)));
(PARI) my(N=30, x='x+O('x^N)); concat([0, 0], Vec(serlaplace(sum(k=0, N\3, (-log(1-x))^(3*k+2)/(3*k+2)!))))
(PARI) Pochhammer(x, n) = prod(k=0, n-1, x+k);
a(n) = my(w=(-1+sqrt(3)*I)/2); round(Pochhammer(1, n)+w*Pochhammer(w, n)+w^2*Pochhammer(w^2, n))/3;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 14 2022
STATUS
approved