OFFSET
2,1
LINKS
Stefano Spezia, Table of n, a(n) for n = 2..1600
FORMULA
Conjecture: D-finite with recurrence -2*(n+3)*(139*n-175)*a(n) +(1279*n^2+1334*n-1089)*a(n-1) -2*(167*n+121)*(2*n-3)*a(n-2) +12*(111*n^2+456*n+229)=0. - R. J. Mathar, May 06 2026
a(n) = 2*binomial(2*n+2, n-1) + binomial(2*n, n-2) - 4. - Christian Krause, May 11 2026
G.f.: 4 + 9/sqrt(1 - 4*x) - 4/(1 - x) + (2*(sqrt(1 - 4*x) - 1) + x*(3 + sqrt(1 - 4*x) + (2 + 4*sqrt(1 - 4*x))*x + 4*x^3))/(2*x^3). - Stefano Spezia, May 11 2026
MAPLE
A027174 := proc(n)
A027170(2*n, n-2) ;
end proc:
seq(A027174(n), n=2..50) ; # R. J. Mathar, May 06 2026
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
EXTENSIONS
a(24)-a(26) from Stefano Spezia, May 12 2026
STATUS
approved
