For n >= 2, a(n) = b(n+1)+b(n)+b(n-1), where the b(i) are the ménage numbers A000179; a(0)=a(1)=1.

A000270

For n >= 2, a(n) = b(n+1)+b(n)+b(n-1), where the b(i) are the ménage numbers A000179; a(0)=a(1)=1.

Terms

    a(0) =1a(1) =1a(2) =0a(3) =3a(4) =16a(5) =95a(6) =672a(7) =5397a(8) =48704a(9) =487917a(10) =5373920a(11) =64547175a(12) =839703696a(13) =11762247419a(14) =176509466560

External references