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 A135627 #33 Nov 06 2018 08:20:36 %S A135627 5,27,495,8127,33550335,8589869055,137438691327,2305843008139952127, %T A135627 2658455991569831744654692615953842175, %U A135627 191561942608236107294793378084303638130997321548169215 %N A135627 Perfect numbers minus 1. %C A135627 Conjecture: every odd prime is a factor of at least one number in this sequence. - _J. Lowell_, Apr 17 2014 %C A135627 a(n) written in base 2 is A138831(n) which is also a member of A138148 (cyclops numbers with binary digits only), assuming there are no odd perfect numbers. - _Omar E. Pol_, Oct 24 2016 [clarified on Nov 03 2018]. %H A135627 G. C. Greubel, <a href="/A135627/b135627.txt">Table of n, a(n) for n = 1..15</a> %F A135627 a(n) = A000396(n) - 1. %t A135627 (# (# + 1))/2 & /@ Select[2^Range[100] - 1, PrimeQ] - 1 (* _G. C. Greubel_, Oct 24 2016, based on _Harvey P. Dale_ code from A000396 *) %Y A135627 Cf. A000396, A065091, A138148, A134808, A138831. %K A135627 nonn %O A135627 1,1 %A A135627 _Omar E. Pol_, Nov 27 2007