a(n) = C(n,6) + C(n,5) + C(n,4) + C(n,3) + C(n,2) + C(n,1).

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =15a(5) =31a(6) =63a(7) =126a(8) =246a(9) =465a(10) =847a(11) =1485a(12) =2509a(13) =4095a(14) =6475a(15) =9948a(16) =14892a(17) =21777a(18) =31179a(19) =43795a(20) =60459a(21) =82159a(22) =110055a(23) =145498a(24) =190050a(25) =245505a(26) =313911a(27) =397593a(28) =499177a(29) =621615