a(n) = 8*n + 4.

Terms

a(0) =4a(1) =12a(2) =20a(3) =28a(4) =36a(5) =44a(6) =52a(7) =60a(8) =68a(9) =76a(10) =84a(11) =92a(12) =100a(13) =108a(14) =116a(15) =124a(16) =132a(17) =140a(18) =148a(19) =156a(20) =164a(21) =172a(22) =180a(23) =188a(24) =196a(25) =204a(26) =212a(27) =220a(28) =228a(29) =236