a(n) is the hafnian of the 2n X 2n symmetric matrix defined by M[i,j] = abs(i - j) if min(i, j) < max(i, j) <= 2*min(i, j), and otherwise 0.

A357420

a(n) is the hafnian of the 2n X 2n symmetric matrix defined by M[i,j] = abs(i - j) if min(i, j) < max(i, j) <= 2*min(i, j), and otherwise 0.

Terms

    a(0) =1a(1) =1a(2) =1a(3) =8a(4) =86a(5) =878a(6) =13730a(7) =348760a(8) =11622396a(9) =509566864a(10) =26894616012

External references