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 A133273 #24 Dec 03 2024 08:25:14
%S A133273 1,10,171,3060,54901,985150,17677791,317215080,5692193641,
%T A133273 102142270450,1832868674451,32889493869660,590178020979421,
%U A133273 10590314883759910,190035489886698951,3410048503076821200,61190837565496082641,1098025027675852666330,19703259660599851911291
%N A133273 Indices of centered decagonal numbers which are also decagonal numbers.
%C A133273 Numbers k such that 80*k^2 - 80*k + 25 is a square.
%C A133273 Also the indices of centered square numbers which are also centered pentagonal numbers. - _Colin Barker_, Jan 01 2015
%H A133273 Colin Barker, <a href="/A133273/b133273.txt">Table of n, a(n) for n = 1..798</a>
%H A133273 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (19,-19,1).
%F A133273 a(n+2) = 18*a(n+1) - a(n) - 8.
%F A133273 a(n+1) = 9*a(n) - 4 + sqrt(80*a(n)^2 - 80*a(n) + 25).
%F A133273 G.f.: x*(-1+9*x)/(-1+x)/(1 - 18*x + x^2). - _R. J. Mathar_, Nov 14 2007
%F A133273 a(n) = 19*a(n-1) - 19*a(n-2) + a(n-3). - _Colin Barker_, Jan 01 2015
%F A133273 Product_{n>=2} (1 - 1/a(n)) = 2/sqrt(5) (= A010532 / 10). - _Amiram Eldar_, Dec 02 2024
%t A133273 LinearRecurrence[{19,-19,1},{1,10,171},20] (* _Harvey P. Dale_, Oct 09 2020 *)
%o A133273 (PARI) Vec(x*(-1+9*x)/((-1+x)*(1-18*x+x^2)) + O(x^100)) \\ _Colin Barker_, Jan 01 2015
%Y A133273 Cf. A001107, A001844, A005891, A010532, A062786, A128922.
%K A133273 nonn,easy
%O A133273 1,2
%A A133273 _Richard Choulet_, Oct 16 2007
%E A133273 More terms from _Paolo P. Lava_, Nov 25 2008