OFFSET
0,2
COMMENTS
The series whose terms are the quotients a(n)/A013709(n) (modified (4n+0) Wallis-Lambert-series-1) is convergent to 4*(1-3/Pi). Proof: Both the Wallis-Lambert-series-1=4/Pi-1 and the elliptic Euler-series=1-2/Pi are absolutely convergent series. Thus any linear combination of the terms of these series will be also absolutely convergent to the value of the linear combination of these series - in this case to 4(1-3/Pi). Q.E.D.
LINKS
Ralf Steiner, Beispiele zur modifizierten Wallis-Lambert-Reihe (in German).
FORMULA
a(n) = 4*A268085(n).
a(n+1) = a(n)*4*(n+1)*(2*n+1)^2/(n*(n+2)^2) for n > 0. - Chai Wah Wu, Jan 28 2016
EXAMPLE
For n=3, a(3)=300.
MATHEMATICA
Table[CatalanNumber[n]^2 (4 n + 0), {n, 0, 20}]
PROG
(PARI) a(n) = 4*n*(binomial(2*n, n)/(n+1))^2; \\ Michel Marcus, Jan 24 2016
(Magma) [Catalan(n)^2*4*n: n in [0..20]]; // Vincenzo Librandi, Jan 24 2016 *)
(Python)
from __future__ import division
A267982_list, b = [0], 4
for n in range(1, 10**2):
A267982_list.append(b)
b = b*4*(n+1)*(2*n+1)**2//(n*(n+2)**2) # Chai Wah Wu, Jan 28 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Steiner, Jan 23 2016
EXTENSIONS
More terms from Vincenzo Librandi, Jan 24 2016
STATUS
approved