Number of n-element sets of singletons or pairs of distinct elements of {1..n} with union {1..n}, or loop-graphs covering n vertices with n edges.

A368597

Number of n-element sets of singletons or pairs of distinct elements of {1..n} with union {1..n}, or loop-graphs covering n vertices with n edges.

Terms

    a(0) =1a(1) =1a(2) =3a(3) =17a(4) =150a(5) =1803a(6) =27364a(7) =501015a(8) =10736010a(9) =263461265a(10) =7283725704a(11) =223967628066

External references