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 A232538 #16 Sep 12 2019 08:47:29 %S A232538 33,136,145,261,897,1441,2016,2241,2353,3808,4320,7201,17101,26937, %T A232538 30721,32896,46593,70561,148960,151633,169345,174592,208801,400401, %U A232538 578593,712801,803800,1040401,1103233,1596673,2265121,2377089,3330001,4357153,5953024,5962321 %N A232538 Numbers n such that (n(n+1)/2) modulo sigma(n) = n. %C A232538 Also numbers n such that antisigma(n) modulo sigma(n) = n. Antisigma(n) = A024816(n) = the sum of the nondivisors of n that are between 1 and n, sigma(n) = A000203(n) = the sum of the divisors of n. %C A232538 Numbers n such that A232324(n) = n. %C A232538 a(19) > 10^5. %F A232538 A232324(a(n)) = n. %e A232538 136 is in sequence because antisigma(136) mod sigma(136) = 9046 mod 270 = 136. %t A232538 Select[Range[6*10^6],Mod[(#(#+1))/2,DivisorSigma[1,#]]==#&] (* _Harvey P. Dale_, Sep 12 2019 *) %o A232538 (PARI) isok(n) = (n*(n+1)/2 - sigma(n)) % sigma(n) == n; \\ _Michel Marcus_, Nov 25 2013 %Y A232538 Cf. A000203, A076617, A024816, A232324, A232540. %K A232538 nonn %O A232538 1,1 %A A232538 _Jaroslav Krizek_, Nov 25 2013 %E A232538 More terms from _Michel Marcus_, Nov 25 2013