OFFSET
0,2
REFERENCES
The right-hand side of a binomial coefficient identity in H. W. Gould, Combinatorial Identities, Morgantown, 1972. (See (3.75) on page 31.)
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..825
FORMULA
From G. C. Greubel, Jun 22 2022: (Start)
a(n) = Sum_{k=0..floor((n-1)/2)} binomial(2*n, 2*k+1)^2.
G.f.: (1/4)*(sqrt(1 + sqrt(1-16*x))/(sqrt(2)*sqrt(1-16*x)) - 1/sqrt(1+4*x)) + (1/(2*Pi))*( EllipticK(16*x) - EllipticK(-16*x)). (End)
MAPLE
A037976 := proc(n)
binomial(4*n, 2*n)/4-(-1)^n*binomial(2*n, n)/4+(1-(-1)^n)*binomial(2*n, n)^2/4 ;
end proc:
seq(A037976(n), n=0..30) ; # R. J. Mathar, Jul 26 2015
MATHEMATICA
With[{B=Binomial}, Table[(1/4)*(B[4*n, 2*n] +B[2*n, n]^2 -2*(-1)^n*B[B[2*n, n] +1, 2]), {n, 0, 30}]] (* G. C. Greubel, Jun 22 2022 *)
PROG
(Magma) [(1/4)*((2*n+1)*Catalan(2*n) -(-1)^n*(n+1)*Catalan(n) +(1-(-1)^n)*(n+1)^2*Catalan(n)^2): n in [0..30]]; // G. C. Greubel, Jun 22 2022
(SageMath) b=binomial; [(1/4)*(b(4*n, 2*n) -(-1)^n*b(2*n, n) +(1-(-1)^n)*b(2*n, n)^2) for n in (0..30)] # G. C. Greubel, Jun 22 2022
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved