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 A181711 #41 Jun 20 2017 23:06:21 %S A181711 18,196,15376,1032256,274810802176,1125882727038976,72057319160283136, %T A181711 4951760152529835082242850816, %U A181711 6129982163463555428116476125461573244012649752219877376 %N A181711 Numbers of the form m*(2^k-1), where m = 2^(k-1)*(2^k-1) is a perfect number (A000396). %C A181711 The associated exponents k are in A000043: 2, 3, 5, 7, 13, 17, 19 ,31, 61, ... %C A181711 One can prove that, if m = 2^(k-1)*(2^k-1) is a perfect number, then m*2^k and m*(2^k-1) are both in A181595. Thus every even term in A000396 is a difference of two terms in A181595. %F A181711 If odd perfect numbers do not exist, then a(n) = A181710(n) - A000396(n). %F A181711 a(n) = A019279(n)*(A000668(n))^2 if there are no odd superperfect numbers. - _César Aguilera_, Jun 13 2017 %e A181711 With k=3, m = 2^(k-1)*(2^k - 1) = 2^2*(8 - 1) = 28 is a perfect number (A000396), so m*(2^k - 1) = 28*7 = 196 is in the sequence. - _Michael B. Porter_, Jul 19 2016 %Y A181711 Cf. A000043, A000396, A181595, A181596, A181701, A181710. %K A181711 nonn %O A181711 1,1 %A A181711 _Vladimir Shevelev_, Nov 07 2010 %E A181711 Definition condensed by _R. J. Mathar_, Dec 05 2010