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 A124260 #11 Dec 26 2020 06:37:58
%S A124260 4,126,12,4,780,94036996914,56,8,9,1111111110,132,12,30940,8108730,
%T A124260 240,16,306,18,380,20,204204,11154,552,24,25,702,27,28,732540,27930,
%U A124260 992,32,1222980,62556901638174,1260,36,1926220,2141490,1560,40,2896404
%N A124260 a(n) = Sum_{k=1..A124259(n)} n^k.
%H A124260 Amiram Eldar, <a href="/A124260/b124260.txt">Table of n, a(n) for n = 1..1589</a>
%F A124260 a(A013929(n)) = A013929(n).
%t A124260 a[n_] := Module[{k = 1, s = n}, While[SquareFreeQ[s], k++; s += n^k]; s]; Array[a, 100] (* _Amiram Eldar_, Dec 26 2020 *)
%o A124260 (PARI) a(n) = my(k=1, s); while (issquarefree(s=sum(i=1, k, n^i)), k++); s; \\ _Michel Marcus_, Dec 26 2020
%Y A124260 Cf. A002378, A013929, A027444, A027445, A124259.
%K A124260 nonn
%O A124260 1,1
%A A124260 _Reinhard Zumkeller_, Oct 23 2006