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 A281265 #11 Apr 17 2017 23:32:54 %S A281265 6160,11697,12220,16005,23500,28917,68908,76245,249424,339825,425500, %T A281265 434784,570405,649990,660825,678376,697851,871585,1017856,1077336, %U A281265 1238380,1252216,1340865,1483785,1568260,1754536,1823925,1899261,2067625,2166136,2362360,2479065 %N A281265 Variation on betrothed numbers. %C A281265 Members of a pair (x,y) such that sigma(x) = sigma(y) = x + y - 1, where sigma = A000203. %C A281265 The first time a pair ordered by its first element is not adjacent is x = 425500, y = 570405 which correspond to a(11) and a(13), respectively. %F A281265 A007992 U A015630. %e A281265 sigma(6160) = sigma(11697) = 6160 + 11697 - 1 = 17856. %p A281265 with(numtheory): P:=proc(q) local a,b,n; for n from 1 to q do %p A281265 a:=sigma(n)-n+1; b:=sigma(a)-a+1; if b=n and a<>b then print(n); %p A281265 fi; od; end: P(10^9); %Y A281265 Cf. A000203, A005276, A007992, A015630. %K A281265 nonn,easy %O A281265 1,1 %A A281265 _Paolo P. Lava_, Apr 13 2017