Double factorial of odd numbers: a(n) = (2*n-1)!! = 1*3*5*...*(2*n-1).

A001147

Double factorial of odd numbers: a(n) = (2*n-1)!! = 1*3*5*...*(2*n-1).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =15a(4) =105a(5) =945a(6) =10395a(7) =135135a(8) =2027025a(9) =34459425a(10) =654729075a(11) =13749310575a(12) =316234143225

External references