312081

Appears in sequences

• a(n) is the hafnian of the 2n X 2n symmetric matrix defined by M[i, j] = i + j - 1.at n=4A357279
• a(n) = 1*binomial(n,2) + 3*binomial(n,3) + 6*binomial(n,4) + 10*binomial(n,5).at n=22A361474