OFFSET
0,3
FORMULA
a(n) = (binomial(2*n, n) + (binomial(n, n/2)*cos(Pi*n/2))^2)/2.
D-finite with recurrence: 2*(2*n+1)*(4*n^2+15*n+13)*(16*(n+1)^2*a(n) - (n+2)^2*a(n+2)) = (n+2)*(4*n^2+7*n+2)*(16*(n+2)^2*a(n+1) - (n+3)^2*a(n+3)).
G.f.: (1/sqrt(1 - 4*x) + 2*K(4*x)/Pi)/2, where K is the complete elliptic integral of the first kind with modulus 4*x. - Benedict W. J. Irwin, Oct 19 2016
D-finite with recurrence n^2*(n-1)*a(n) -2*(3*n-4)*(n-1)^2*a(n-1) +4*(-19*n^2+64*n-56)*a(n-2) +16*(4*n^3-11*n^2-16*n+49)*a(n-3) -64*(4*n-15)*(n-3)^2*a(n-4) +256*(2*n-9)*(n-4)^2*a(n-5)=0. - R. J. Mathar, Jan 11 2024
MAPLE
A277247 := proc(n)
add(binomial(n, k)^2, k=0..floor(n/2)) ;
end proc:
seq(A277247(n), n=0..50) ; # R. J. Mathar, Jan 11 2024
MATHEMATICA
Table[(Binomial[2 n, n] + (Binomial[n, n/2] Cos[Pi n/2])^2)/2, {n, 0, 30}]
CoefficientList[Series[(1/Sqrt[1-4x]+(2EllipticK[16 x^2])/Pi)/2, {x, 0, 20}], x] (* Benedict W. J. Irwin, Oct 19 2016 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Reshetnikov, Oct 06 2016
STATUS
approved