a(n) is the hafnian of the 2n X 2n symmetric matrix defined by M[i,j] = floor(i*j/3).

A358158

a(n) is the hafnian of the 2n X 2n symmetric matrix defined by M[i,j] = floor(i*j/3).

Terms

    a(0) =1a(1) =0a(2) =4a(3) =238a(4) =31992a(5) =9390096a(6) =4755878928

External references