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 A254857 #8 Jun 13 2015 00:55:24 %S A254857 1,8,736,5461,496133,3680776,334392976,2480837633,225380369761, %T A254857 1672080883936,151906034826008,1126980034935301,102384442092359701, %U A254857 759582871465509008,69006962064215612536,511957728387718136161,46510590046839230489633,345058749350450558263576 %N A254857 Octagonal numbers (A000567) that are also centered heptagonal numbers (A069099). %H A254857 Colin Barker, <a href="/A254857/b254857.txt">Table of n, a(n) for n = 1..708</a> %H A254857 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,674,-674,-1,1). %F A254857 a(n) = a(n-1)+674*a(n-2)-674*a(n-3)-a(n-4)+a(n-5). %F A254857 G.f.: -x*(x^4+7*x^3+54*x^2+7*x+1) / ((x-1)*(x^2-26*x+1)*(x^2+26*x+1)). %e A254857 736 is in the sequence because it is the 16th octagonal number and the 15th centered heptagonal number. %o A254857 (PARI) Vec(-x*(x^4+7*x^3+54*x^2+7*x+1)/((x-1)*(x^2-26*x+1)*(x^2+26*x+1)) + O(x^100)) %Y A254857 Cf. A000567, A069099, A254855, A254856. %K A254857 nonn,easy %O A254857 1,2 %A A254857 _Colin Barker_, Feb 08 2015