OFFSET
1,1
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Alain Goupil, Decomposition of certain products of conjugacy classes of S_n, J. Combin. Theory, A 66 (1994), 102-117.
FORMULA
a(n) = b(n, 2*n+2) where b(k, m) = (2 * m! / (k^2 * (m-k)^2)) * ((m / (m+1)) * (1 + (-1)^(k+1) / binomial(m, k)) + ((k+1) / binomial(m, k)) * Sum_{j=0..k-1} (j+1) / (binomial(k - 1, j) * binomial(k, j))) [from Goupil]. - Sean A. Irvine, Nov 23 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Nov 23 2017
STATUS
approved