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 A076270 #7 Jun 12 2015 20:08:19
%S A076270 1,4,10,13,28,40,82,91,121,244,364,730,757,820,1093,2188,3280,6562,
%T A076270 6643,7381,9841,19684,20440,29524,59050,59293,66430,88573,177148,
%U A076270 265720,531442,532171,538084,551881,597871,797161,1594324,2391484,4782970,4785157,5380840
%N A076270 Numbers of the form (3^{mr}-1)/(3^r-1) for positive integers m, r.
%H A076270 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 A076270 f := proc(p) local m,r,t1; t1 := {}; for m from 1 to 10 do for r from 1 to 10 do t1 := {op(t1), (p^(m*r)-1)/(p^r-1)}; od: od: sort(convert(t1,list)); end; f(3); # very crude!
%Y A076270 Cf. A064896 (k=2), A076270 (k=3), A076275 (k=4), A076284 (k=5), A076286 (k=7), A076287 (k=8), A076288 (k=9), A076289 (k=10).
%K A076270 nonn
%O A076270 1,2
%A A076270 _N. J. A. Sloane_, Nov 06 2002