a(n) = solution to the postage stamp problem with 2 denominations and n stamps.

Terms

a(0) =2a(1) =4a(2) =7a(3) =10a(4) =14a(5) =18a(6) =23a(7) =28a(8) =34a(9) =40a(10) =47a(11) =54a(12) =62a(13) =70a(14) =79a(15) =88a(16) =98a(17) =108a(18) =119a(19) =130a(20) =142a(21) =154a(22) =167a(23) =180a(24) =194a(25) =208a(26) =223a(27) =238a(28) =254a(29) =270