>I think it should be >binomial(2n-2, n-1) = binomial(2^(m+1)-4, 2^m-2) >instead of >binomial(2n-2, n-1) = binomial(2^(m+1)-4, 2^m-1) Emmanuel, C(n) = (1/(n+1))*binomial(2*n, n), so C(2^m-1) = (1/2^m)*binomial(2^(m+1)-2, 2^m-1). Ed Jeffery