a(n) = (8*n+3)^3.

Terms

a(0) =27a(1) =1331a(2) =6859a(3) =19683a(4) =42875a(5) =79507a(6) =132651a(7) =205379a(8) =300763a(9) =421875a(10) =571787a(11) =753571a(12) =970299a(13) =1225043a(14) =1520875a(15) =1860867a(16) =2248091a(17) =2685619a(18) =3176523a(19) =3723875a(20) =4330747a(21) =5000211a(22) =5735339a(23) =6539203a(24) =7414875