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 A254284 #8 Nov 11 2020 12:14:35
%S A254284 1,36,133,6888,25705,1336140,4986541,259204176,967363153,50284273908,
%T A254284 187663465045,9754889933880,36405744855481,1892398362898716,
%U A254284 7062526838498173,367115527512416928,1370093800923789985,71218519939045985220,265791134852376758821
%N A254284 Indices of centered triangular numbers (A005448) which are also hexagonal numbers (A000384).
%C A254284 Also positive integers y in the solutions to 4*x^2 - 3*y^2 - 2*x + 3*y - 2 = 0, the corresponding values of x being A254283.
%H A254284 Colin Barker, <a href="/A254284/b254284.txt">Table of n, a(n) for n = 1..875</a>
%H A254284 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,194,-194,-1,1).
%F A254284 a(n) = a(n-1)+194*a(n-2)-194*a(n-3)-a(n-4)+a(n-5).
%F A254284 G.f.: x*(35*x^3+97*x^2-35*x-1) / ((x-1)*(x^2-14*x+1)*(x^2+14*x+1)).
%e A254284 36 is in the sequence because the 36th centered triangular number is 1891, which is also the 31st hexagonal number.
%t A254284 LinearRecurrence[{1,194,-194,-1,1},{1,36,133,6888,25705},20] (* _Harvey P. Dale_, Nov 11 2020 *)
%o A254284 (PARI) Vec(x*(35*x^3+97*x^2-35*x-1)/((x-1)*(x^2-14*x+1)*(x^2+14*x+1)) + O(x^100))
%Y A254284 Cf. A000384, A005448, A254283, A254285.
%K A254284 nonn,easy
%O A254284 1,2
%A A254284 _Colin Barker_, Jan 28 2015