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 A254711 #5 Jun 13 2015 00:55:24 %S A254711 1,5,145,925,28085,179401,5448301,34802825,1056942265,6751568605, %T A254711 205041351065,1309769506501,39776965164301,254088532692545, %U A254711 7716526200523285,49291865572847185,1496966305936352945,9562367832599661301,290403746825451948001 %N A254711 Pentagonal numbers (A000326) which are also centered square numbers (A001844). %H A254711 Colin Barker, <a href="/A254711/b254711.txt">Table of n, a(n) for n = 1..875</a> %H A254711 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,194,-194,-1,1). %F A254711 a(n) = a(n-1)+194*a(n-2)-194*a(n-3)-a(n-4)+a(n-5). %F A254711 G.f.: -x*(x^4+4*x^3-54*x^2+4*x+1) / ((x-1)*(x^2-14*x+1)*(x^2+14*x+1)). %e A254711 145 is in the sequence because it is the 10th pentagonal number and the 9th centered square number. %o A254711 (PARI) Vec(-x*(x^4+4*x^3-54*x^2+4*x+1)/((x-1)*(x^2-14*x+1)*(x^2+14*x+1)) + O(x^100)) %Y A254711 Cf. A000326, A001844, A254709, A254710. %K A254711 nonn,easy %O A254711 1,2 %A A254711 _Colin Barker_, Feb 06 2015