a(n) = C(3,n) DELTA C(0,n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =5a(5) =1a(6) =25a(7) =33a(8) =9a(9) =1a(10) =172a(11) =238a(12) =78a(13) =13a(14) =1a(15) =1201a(16) =1745a(17) =667a(18) =139a(19) =17a(20) =1a(21) =8404a(22) =12807a(23) =5583a(24) =1376a(25) =216a(26) =21a(27) =1a(28) =58825a(29) =93841