a(n) = 4^(n-1) - 3*3^(n-1) + 3*2^(n-1) - 1 (essentially Stirling numbers of second kind).

A028244

a(n) = 4^(n-1) - 3*3^(n-1) + 3*2^(n-1) - 1 (essentially Stirling numbers of second kind).

Terms

    a(0) =0a(1) =0a(2) =0a(3) =6a(4) =60a(5) =390a(6) =2100a(7) =10206a(8) =46620a(9) =204630a(10) =874500a(11) =3669006a(12) =15195180a(13) =62350470a(14) =254135700a(15) =1030793406a(16) =4166023740a(17) =16792841910a(18) =67558001700a(19) =271392695406

External references