a(n) = (6*n + 3)^3.

Terms

a(0) =27a(1) =729a(2) =3375a(3) =9261a(4) =19683a(5) =35937a(6) =59319a(7) =91125a(8) =132651a(9) =185193a(10) =250047a(11) =328509a(12) =421875a(13) =531441a(14) =658503a(15) =804357a(16) =970299a(17) =1157625a(18) =1367631a(19) =1601613a(20) =1860867a(21) =2146689a(22) =2460375a(23) =2803221a(24) =3176523a(25) =3581577a(26) =4019679a(27) =4492125a(28) =5000211a(29) =5545233