This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A048721 #14 Jul 28 2022 20:33:08 %S A048721 0,1,3,7,23,151,4247,1052823,8590987415,18014407100469399, %T A048721 309485009839359475825250455, %U A048721 11150372599265311880252868975683656578240663,6901746346790563787434755873427398051716420852423255530846180802039959 %N A048721 Binary packing of Fibonacci sequence A000045. %C A048721 Prime values of a(n) begin 3, 7, 23, 151, i.e., for n = 2, 3, 4, 5. Semiprime values of a(n) begin 4247 = 31 * 137, 1052823 = 3 * 350941, i.e., for n = 6, 7. - _Jonathan Vos Post_, May 09 2005 %F A048721 a(0) = 0, a(n) = a(n-1)+(2^(Fib(n+1)-1)). %Y A048721 Cf. A000045, A005203, A048722, A036571. %K A048721 nonn %O A048721 0,3 %A A048721 Antti Karttunen, Mar 30 1999