OFFSET
0,2
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..830
MATHEMATICA
T[_, 0] = 1; T[n_, k_] := 1/n DivisorSum[n, If[GCD[k, #] == #, EulerPhi[#]*Binomial[n/#, k/#]^2, 0] &];
Table[T[n, k], {n, 0, 11}, {k, 0, n}] // Flatten (* A123610 *)
Table[T[2*n, n], {n, 0, 50}] (* A123617 *)
Table[T[2*n + 2, n], {n, 0, 50}] (* A123618 *)
Table[T[2*n + 2, n]/(n+1), {n, 0, 50}] (* A123619 *)
(* G. C. Greubel, Oct 26 2017 *)
PROG
(PARI) {a(n)=if(n==0, 1, (1/2/n)*sumdiv(2*n, d, if(gcd(n, d)==d, eulerphi(d)*binomial(2*n/d, n/d)^2, 0)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Oct 03 2006
STATUS
approved