OFFSET
0,2
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Marcia Ascher, Mu torere: an analysis of a Maori game, Math. Mag. 60 (1987), no. 2, 90-100.
R. K. Guy & N. J. A. Sloane, Correspondence, 1985
MATHEMATICA
a[0] = 1; a[n_] := (1/2)*(Binomial[ 2*Quotient[n, 2], Quotient[n, 2]] + 2*(Binomial[ 2n-1, n] + Binomial[ n-1, Quotient[n, 2]]) + Sum[ EulerPhi[n/k] * Binomial[2k, k]/(2n), {k, Divisors[n]}]); Table[ a[n], {n, 0, 24}] (* Jean-François Alcover, Jan 27 2012, after PARI *)
PROG
(PARI) C(n, k)=if(k<0||k>n, 0, n!/k!/(n-k)!);
a(n)= (1/2) *( C(2*(n\2), n\2) + 2*(C(2*n-1, n)+C(n-1, n\2)) + if(n<1, n >= 0, sumdiv(n, k, eulerphi(n/k)*C(2*k, k))/(2*n)) )
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
EXTENSIONS
Better description and more terms from Michael Somos
STATUS
approved