Hex (or centered hexagonal) numbers: 3*n*(n+1)+1 (crystal ball sequence for hexagonal lattice).

Terms

a(0) =1a(1) =7a(2) =19a(3) =37a(4) =61a(5) =91a(6) =127a(7) =169a(8) =217a(9) =271a(10) =331a(11) =397a(12) =469a(13) =547a(14) =631a(15) =721a(16) =817a(17) =919a(18) =1027a(19) =1141a(20) =1261a(21) =1387a(22) =1519a(23) =1657a(24) =1801a(25) =1951a(26) =2107a(27) =2269a(28) =2437a(29) =2611