Number of powerful numbers <= 10^n.

Terms

a(0) =1a(1) =4a(2) =14a(3) =54a(4) =185a(5) =619a(6) =2027a(7) =6553a(8) =21044a(9) =67231a(10) =214122a(11) =680330a(12) =2158391a(13) =6840384a(14) =21663503a(15) =68575557a(16) =217004842a(17) =686552743a(18) =2171766332a(19) =6869227848a(20) =21725636644a(21) =68709456167a(22) =217293374285a(23) =687174291753