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

Terms

a(0) =1a(1) =12a(2) =105a(3) =360a(4) =858a(5) =1680a(6) =2907a(7) =4620a(8) =6900a(9) =9828a(10) =13485a(11) =17952a(12) =23310a(13) =29640a(14) =37023a(15) =45540a(16) =55272a(17) =66300a(18) =78705a(19) =92568a(20) =107970a(21) =124992a(22) =143715a(23) =164220a(24) =186588a(25) =210900a(26) =237237a(27) =265680a(28) =296310a(29) =329208