a(0)=1; a(1)=1; for n>1, a(n) = a(n-1) + 3*n*a(n-2).

Terms

a(0) =1a(1) =1a(2) =7a(3) =16a(4) =100a(5) =340a(6) =2140a(7) =9280a(8) =60640a(9) =311200a(10) =2130400a(11) =12400000a(12) =89094400a(13) =572694400a(14) =4314659200a(15) =30085907200a(16) =237189548800