a(n) = Sum_{k=1..n} 2^nonprime(k).

Terms

a(0) =2a(1) =18a(2) =82a(3) =338a(4) =850a(5) =1874a(6) =5970a(7) =22354a(8) =55122a(9) =120658a(10) =382802a(11) =1431378a(12) =3528530a(13) =7722834a(14) =24500050a(15) =58054482a(16) =125163346a(17) =259381074a(18) =527816530a(19) =1601558354a(20) =5896525650a(21) =14486460242a(22) =31666329426a(23) =66026067794a(24) =134745544530a(25) =409623451474a(26) =959379265362