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 A254136 #9 Mar 24 2024 16:59:18
%S A254136 1,73,889,84049,1025713,96992281,1183671721,111929008033,
%T A254136 1365956140129,129165978277609,1576312202036953,149057427003352561,
%U A254136 1819062915194503441,172012141595890577593,2099197027822254933769,198501862344230723189569,2422471551043966999065793
%N A254136 Indices of pentagonal numbers (A000326) which are also centered hexagonal numbers (A003215).
%C A254136 Also positive integers x in the solutions to 3*x^2 - 6*y^2 - x + 6*y - 2 = 0, the corresponding values of y being A254137.
%H A254136 Colin Barker, <a href="/A254136/b254136.txt">Table of n, a(n) for n = 1..653</a>
%H A254136 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,1154,-1154,-1,1).
%F A254136 a(n) = a(n-1)+1154*a(n-2)-1154*a(n-3)-a(n-4)+a(n-5).
%F A254136 G.f.: -x*(x^4+72*x^3-338*x^2+72*x+1) / ((x-1)*(x^2-34*x+1)*(x^2+34*x+1)).
%e A254136 73 is in the sequence because the 73rd pentagonal number is 7957, which is also the 52nd centered hexagonal number.
%t A254136 LinearRecurrence[{1,1154,-1154,-1,1},{1,73,889,84049,1025713},20] (* _Harvey P. Dale_, Mar 24 2024 *)
%o A254136 (PARI) Vec(-x*(x^4+72*x^3-338*x^2+72*x+1)/((x-1)*(x^2-34*x+1)*(x^2+34*x+1)) + O(x^100))
%Y A254136 Cf. A000326, A003215, A254137, A254138.
%K A254136 nonn,easy
%O A254136 1,2
%A A254136 _Colin Barker_, Jan 26 2015