3061162125

Appears in sequences

• a(n) = (n-1)!! - (n-2)!!.at n=18A007911
• a(n) = (2*n+2)!! - (2*n+1)!!.at n=9A129890
• Triangle read by rows: T(n,k) (1 <= k <= n-1, n >= 2) = d(2*(n-k)-1)*(d(2*n-2)/d(2*(n-k)-2) - d(2*n-3)/d(2*(n-k)-3)), where d = A006882 is the double factorial function.at n=54A202212
• a(n) = (n!)*2^(n-1)*mu_h(n) where mu_h is the hypergeometric Moebius function associated to the Dirichlet character modulo 4 h={1,0,-1,0,1,...} (see comment).at n=10A298510