OFFSET
0,2
COMMENTS
Let ((1 + k*x)/(1 - k*x))^(m/k) = a(0) + a(1)*x + a(2)*x^2 + ... then n*a(n) = 2*m*a(n-1) + k^2*(n-2)*a(n-2) for n > 1.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..3000
FORMULA
n*a(n) = 6*a(n-1) + 4*(n-2)*a(n-2) for n > 1.
a(n) ~ 2^(n + 5/2) * sqrt(n/Pi). - Vaclav Kotesovec, May 28 2018
MATHEMATICA
CoefficientList[Series[((1+2*x)/(1-2*x))^(3/2), {x, 0, 40}], x] (* G. C. Greubel, Jun 07 2023 *)
PROG
(PARI) N=66; x='x+O('x^N); Vec(((1+2*x)/(1-2*x))^(3/2))
(Magma) [n le 2 select 6^(n-1) else 2*(3*Self(n-1) + 2*(n-3)*Self(n-2))/(n-1): n in [1..40]]; // G. C. Greubel, Jun 07 2023
(SageMath)
@CachedFunction
def a(n): # b = A305031
if n<2: return 6^n
else: return 2*(3*a(n-1) + 2*(n-2)*a(n-2))//n
[a(n) for n in range(41)] # G. C. Greubel, Jun 07 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 24 2018
STATUS
approved