a(n) = number of special odd permutations of 2*n+1.

A003110

a(n) = number of special odd permutations of 2*n+1.

Terms

    a(0) =0a(1) =2a(2) =2a(3) =108a(4) =2028a(5) =32870a(6) =1213110a(7) =46493784a(8) =2310521000a(9) =137466038346

External references