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 A219053 #17 Apr 22 2013 03:03:08 %S A219053 3,19,131,139,649,3649,4181,5881,13369,29501,65789,37548761,63919409, %T A219053 2471800109 %N A219053 Numbers which are the sum of their proper divisors and their anti-divisors. %C A219053 a(15) > 10^10. - _Donovan Johnson_, Apr 19 2013 %e A219053 The proper divisors of 649 are 1, 11, 59 and its anti-divisors are 2, 3, 22, 118, 433. Their sum 1+11+59+2+3+22+118+433 is equal to 649. %p A219053 with(numtheory); A219053:=proc(q) local a,k,n; %p A219053 for n from 1 to q do a:=0; %p A219053 for k from 2 to n-1 do if abs((n mod k)-k/2)<1 then a:=a+k; fi; od; %p A219053 if 2*n=sigma(n)+a then print(n); fi; od; end: A219053(10^6); %Y A219053 Cf. A000005, A000396, A001065, A066272, A066417, A073930. %K A219053 nonn,more %O A219053 1,1 %A A219053 _Paolo P. Lava_, Apr 17 2013 %E A219053 a(12)-a(14) from _Donovan Johnson_, Apr 19 2013