A246689 - OEIS

%I #31 Feb 25 2023 18:08:45

%S 1,1,3,13,61,381,2791,22513,210393,2183401,24575851,305067621,

%T 4097726293,58876485253,910581818511,15005958062761,261751577640241,

%U 4844661893762193,94564968066402643,1938366513866527741,41760228574294689261,941821175462309114701

%N Expansion of e.g.f. 1/(1 - x^3)^(1 + 1/x + 1/x^2).

%C Compare with A193281.

%H Seiichi Manyama, <a href="/A246689/b246689.txt">Table of n, a(n) for n = 0..448</a>

%F E.g.f.: A(x) = 1/(1 - x^3)^(1 + 1/x + 1/x^2)  = exp( Sum_{n>=1} x^n/A008620(n-1) ) = 1 + x + 3*x^2/2! + 13*x^3/3! + 61*x^4/4! + ....

%F A(x) = Sum_{n>=0} (x^n/n!)*Product {k = 1..n} (1 + x + k*x^2).

%F It appears that a(n) == 1 (mod n*(n-1)).

%F a(n) ~ n! * (n^2 / 54) * (1 + 6*log(n)/n). - _Vaclav Kotesovec_, Sep 01 2014

%F a(0) = 1; a(n) = (n-1)! * Sum_{k=1..n} k/A008620(k-1) * a(n-k)/(n-k)!. - _Seiichi Manyama_, Apr 30 2022

%p seq(coeftayl(n!/(1-x^3)^(1+1/x+1/x^2), x = 0, n), n = 0..10);

%t CoefficientList[Series[1/(1 - x^3)^(1 + 1/x + 1/x^2), {x, 0, 20}], x] * Range[0, 20]! (* _Vaclav Kotesovec_, Sep 01 2014 *)

%o (PARI) my(x='x+O('x^66)); Vec(serlaplace(1/(1 - x^3)^(1 + 1/x + 1/x^2))) \\ _Joerg Arndt_, Sep 01 2014

%o (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=(i-1)!*sum(j=1, i, j/((j+2)\3)*v[i-j+1]/(i-j)!)); v; \\ _Seiichi Manyama_, Apr 30 2022

%Y Cf. A008620, A193281.

%K nonn,easy

%O 0,3

%A _Peter Bala_, Sep 01 2014