a(n) = Bell(n^2), where Bell(n) are the Bell numbers, cf. A000110.

A068939

a(n) = Bell(n^2), where Bell(n) are the Bell numbers, cf. A000110.

Terms

    a(0) =1a(1) =1a(2) =15a(3) =21147a(4) =10480142147

External references