68918850domain: NAppears in sequencesa(n) = (2*n)!/(n!*2^(n-1)).at n=9A097801a(1) = 1, a(2) = -1, a(3) = 2; for n > 3, a(n) = -(2*n-5)*a(n-1).at n=10A129779Irregular triangle T(n,k) read by rows of the reduced coefficients of Pi^(2*k) in the expansion of Sum_{k>=1} (1 / (4*k^2-1)^n).at n=30A382782