A357830 a(n) = Sum_{k=0..floor((n-2)/3)} |Stirling1(n,3*k+2)|.

0, 0, 1, 3, 11, 51, 289, 1939, 15029, 132069, 1296771, 14063721, 166897059, 2150579067, 29895590361, 445871456667, 7100686041813, 120249378265653, 2157637558311963, 40887284144179473, 815949872494416387, 17103401793743095467, 375692072337527815233

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

Cf. A357828, A357829.

Sequence in context: A132006 A367011 A020043 * A184819 A113712 A056199

Adjacent sequences: A357827 A357828 A357829 * A357831 A357832 A357833

Keyword

nonn

Author

Seiichi Manyama, Oct 14 2022

Status

approved