OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..205
FORMULA
a(n) ~ 3^(3*n - 3/2) * n^(2*n - 1) / (2^(n-1) * exp(2*n - 1)). - Vaclav Kotesovec, Apr 06 2019
a(n) = ( 3*(3*n-4)*(3*n-8)*(9*n^2 - 21*n + 11)*a(n-1) + 3*(3*n-2)*a(n-2) - (3*n-5)*(3*n-2)*a(n-3) )/(2*(3*n-5)*(3*n-8)), with a(0) = 1, a(1) = 2, a(3) = 30. - G. C. Greubel, Oct 09 2023
MATHEMATICA
a[n_]:= a[n]= If[n==0, 1, If[n<3, 2*(15)^(n-1), (3*(3*n-4)*(3*n-8)*(9*n^2- 21*n+11)*a[n-1] +3*(3*n-2)*a[n-2] -(3*n-5)*(3*n-2)*a[n-3])/(2*(3*n-5)*(3*n-8))]];
Table[a[n], {n, 0, 30}] (* G. C. Greubel, Oct 09 2023 *)
PROG
(Magma) I:=[1, 2, 30]; [n le 3 select I[n] else ( 3*(3*n-7)*(3*n-11)*(9*n^2 - 39*n + 41)*Self(n-1) + 3*(3*n-5)*Self(n-2) - (3*n-8)*(3*n-5)*Self(n-3) )/(2*(3*n-8)*(3*n-11)): n in [1..30]]; // G. C. Greubel, Oct 09 2023
(SageMath)
@CachedFunction
def a(n): # A144503
if (n<3): return (1, 2, 30)[n]
else: return ( 3*(3*n-4)*(3*n-8)*(9*n^2 - 21*n + 11)*a(n-1) + 3*(3*n-2)*a(n-2) - (3*n-5)*(3*n-2)*a(n-3) )/(2*(3*n-5)*(3*n-8))
[a(n) for n in range(31)] # G. C. Greubel, Oct 09 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
David Applegate and N. J. A. Sloane, Dec 13 2008
STATUS
approved