a(n) = 3^4 * binomial(n+3, 4).

Terms

a(0) =81a(1) =405a(2) =1215a(3) =2835a(4) =5670a(5) =10206a(6) =17010a(7) =26730a(8) =40095a(9) =57915a(10) =81081a(11) =110565a(12) =147420a(13) =192780a(14) =247860a(15) =313956a(16) =392445a(17) =484785a(18) =592515a(19) =717255a(20) =860706a(21) =1024650a(22) =1210950a(23) =1421550a(24) =1658475a(25) =1923831a(26) =2219805a(27) =2548665a(28) =2912760a(29) =3314520