a(n) = -(-1)^n*2*(2*n+1)!*Bernoulli(2*n)/(n!*2^n).

A004193

a(n) = -(-1)^n*2*(2*n+1)!*Bernoulli(2*n)/(n!*2^n).

Terms

    a(0) =1a(1) =1a(2) =5a(3) =63a(4) =1575a(5) =68409a(6) =4729725a(7) =488783295a(8) =71982456975

External references