a(n) = C(n,7) + 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) =127a(8) =254a(9) =501a(10) =967a(11) =1815a(12) =3301a(13) =5811a(14) =9907a(15) =16383a(16) =26332a(17) =41225a(18) =63003a(19) =94183a(20) =137979a(21) =198439a(22) =280599a(23) =390655a(24) =536154a(25) =726205a(26) =971711a(27) =1285623a(28) =1683217a(29) =2182395