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 A076286 #9 Aug 27 2018 22:31:40
%S A076286 1,8,50,57,344,400,2402,2451,2801,16808,19608,117650,117993,120100,
%T A076286 137257,823544,960800,5764802,5767203,5884901,6725601,40353608,
%U A076286 40471600,47079208,282475250,282492057,288360150,329554457,1977326744,2306881200,13841287202
%N A076286 Numbers of the form (7^{mr}-1)/(7^r-1) for positive integers m, r.
%H A076286 Robert Israel, <a href="/A076286/b076286.txt">Table of n, a(n) for n = 1..8539</a>
%H A076286 T. Chinburg and M. Henriksen, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa29/aa2932.pdf">Sums of k-th powers in the ring of polynomials with integer coefficients</a>, Acta Arithmetica, 29 (1976), 227-250.
%p A076286 [1,seq(seq((7^(d+r)-1)/(7^r-1),r = sort(convert(numtheory:-divisors(d),list),`>`)),d=1..20)]; # _Robert Israel_, Aug 27 2018
%Y A076286 Cf. A064896 (k=2), A076270 (k=3), A076275 (k=4), A076284 (k=5), A076285 (k=6), A076287 (k=8), A076288 (k=9), A076289 (k=10).
%K A076286 nonn
%O A076286 1,2
%A A076286 _N. J. A. Sloane_, Nov 06 2002