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 A262613 #35 Dec 15 2024 07:26:17
%S A262613 1,3,6,8,28,24,36,42,48,90,72,80,144,96,168,217,182,312,180,192,372,
%T A262613 216,576,456,280,588,336,352,864,576,720,855,558,756,702,936,1120,600,
%U A262613 1080,1116,1024,2016,1008,816,1296,1152,2016,2072,1178,1860,1344,1120,3600
%N A262613 Sum of divisors of n-th generalized pentagonal number.
%C A262613 For a remarkable connection between the sum-of-divisors function (A000203) and the generalized pentagonal numbers (A001318) see A238442.
%H A262613 Antti Karttunen, <a href="/A262613/b262613.txt">Table of n, a(n) for n = 1..5000</a>
%F A262613 a(n) = A000203(A001318(n)).
%F A262613 Sum_{k=1..n} a(k) ~ (9/40) * n^3. - _Amiram Eldar_, Dec 14 2024
%t A262613 DivisorSigma[1, Select[Accumulate[Range[200]]/3, IntegerQ]] (* _G. C. Greubel_, Jun 06 2017 *)
%o A262613 (Scheme)
%o A262613 (define (A262613 n) (A000203 (A001318 n))) ;; Scheme-program for A000203 given in that entry.
%o A262613 ;; This uses memoization-macro definec:
%o A262613 (definec (A001318 n) (if (zero? n) 0 (+ (if (even? n) (/ n 2) n) (A001318 (- n 1)))))
%o A262613 ;; _Antti Karttunen_, Dec 20 2015
%o A262613 (PARI) a(n) = sigma((3*n^2 + 2*n + (n%2) * (2*n + 1)) / 8); \\ _Michel Marcus_, Dec 21 2015
%o A262613 (Magma) [DivisorSigma(1,(3*n^2+2*n+(n mod 2)*(2*n+1)) div 8): n in [1..70]]; // _Vincenzo Librandi_, Dec 21 2015
%Y A262613 Cf. A000203, A001318, A074285, A117948, A196020, A238442.
%K A262613 nonn,easy
%O A262613 1,2
%A A262613 _Omar E. Pol_, Nov 24 2015