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 A320877 #8 Mar 26 2019 14:48:54
%S A320877 1,5,13,45,173,2221,10413,141485,665773,9054381,545925293,2693408941,
%T A320877 140132362413,2339155617965,11135248640173,151872736995501,
%U A320877 9159071991736493,585619824295159981,2891462833508853933,150465415423185266861,2511648656858007873709,11956381622597298301101
%N A320877 a(n) = 1 + Sum_{k=1..n} 2^prime(k).
%C A320877 Indices of noncomposite terms are 0, 1, 2, 4, 5, 8, 43, 127, 251, ...
%F A320877 a(n) = A076793(n) + 1.
%t A320877 Join[{1},Accumulate[2^Prime[Range[30]]]+1] (* _Harvey P. Dale_, Mar 26 2019 *)
%o A320877 (PARI) apply( A320877(n)=1+sum(k=1,n,2^prime(k)), [0..30])
%Y A320877 Cf. A076793.
%K A320877 nonn
%O A320877 0,2
%A A320877 _M. F. Hasler_, Oct 30 2018