a(n) is the hafnian of the 2n X 2n symmetric matrix whose generic element M[i,j] is equal to the digital root of i*j.

A357421

a(n) is the hafnian of the 2n X 2n symmetric matrix whose generic element M[i,j] is equal to the digital root of i*j.

Terms

    a(0) =1a(1) =2a(2) =54a(3) =1377a(4) =55350a(5) =4164534a(6) =217595322a(7) =11974135554a(8) =999599777190

External references