a(n) = (1/2) * (number of n X n 0..9 matrices with MM' mod 10 = I).

A071308

a(n) = (1/2) * (number of n X n 0..9 matrices with MM' mod 10 = I).

Terms

    a(0) =1a(1) =8a(2) =720a(3) =691200a(4) =6739200000

External references