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 A242962 #9 Sep 08 2022 08:46:08 %S A242962 0,0,0,1,6,3,8,15,13,18,12,28,14,24,24,31,18,39,20,42,32,36,24,60,31, %T A242962 42,40,56,30,72,32,63,48,54,48,91,38,60,56,90,42,96,44,84,78,72,48, %U A242962 124,57,93,72,98,54,120,72,120,80,90,60,168,62,96,104,127,84 %N A242962 a(1) = a(2) = 0; for n >= 3: a(n) = (n*(n+1)/2) mod antisigma(n) = A000217(n) mod A024816(n). %C A242962 A000217(n) = triangular numbers, A024816(n) = sum of numbers less than n which do not divide n. %C A242962 a(n) = sigma(n) = A000203(n) for n = 5 and n>= 7 (see A242963). %H A242962 Michael De Vlieger, <a href="/A242962/b242962.txt">Table of n, a(n) for n = 1..10000</a> %e A242962 a(6) = 3 because A000217(6) mod A024816(6) = 21 mod 9 = 3. %t A242962 Array[If[# < 3, 0, Mod[PolygonalNumber@ #, Total@ Complement[Range@ #, Divisors@ #]]] &, 65] (* _Michael De Vlieger_, Jan 28 2020 *) %o A242962 (Magma) [((n*(n+1)div 2) mod (n*(n+1)div 2-SumOfDivisors(n))): n in [3..1000]] %Y A242962 Cf. A000217, A002961, A024816, A242963, A243117, A243118. %K A242962 nonn %O A242962 1,5 %A A242962 _Jaroslav Krizek_, May 29 2014