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 A057613 #8 Nov 24 2021 19:16:32 %S A057613 1,3,7,15,31,63,127,511,1023,4095,8191,131071,524287,2097151,4194303, %T A057613 8388607,33554431,67108863,8589934591 %N A057613 Numbers that are both lucky numbers (A000959) and of form 2^k-1 (A000225). %C A057613 a(20) >= 17179869183 = 2^34 - 1, if it exists. - _Kevin P. Thompson_, Nov 24 2021 %e A057613 a(7) = 127 since A000959(27) = A000225(7) = 127 and it is the 7th such number with this property. %Y A057613 Cf. A000959, A000225. %K A057613 nonn,more %O A057613 1,2 %A A057613 _Naohiro Nomoto_, Oct 09 2000 %E A057613 More terms from Mark Weston (mweston(AT)uvic.ca), Oct 16 2001 %E A057613 a(18) from _Giovanni Resta_, May 10 2020 %E A057613 a(19) from _Kevin P. Thompson_, Nov 24 2021