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 A273366 #24 May 21 2024 12:09:00
%S A273366 2,22,62,122,202,302,422,562,722,902,1102,1322,1562,1822,2102,2402,
%T A273366 2722,3062,3422,3802,4202,4622,5062,5522,6002,6502,7022,7562,8122,
%U A273366 8702,9302,9922,10562,11222,11902,12602,13322,14062,14822,15602
%N A273366 a(n) = 10*n^2 + 10*n + 2.
%C A273366 These are the numbers k such that 10*k+5 is a perfect square.
%H A273366 G. C. Greubel, <a href="/A273366/b273366.txt">Table of n, a(n) for n = 0..1000</a>
%H A273366 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A273366 G.f.: 2*(x^2+8x+1)/(1-x)^3.
%F A273366 From _G. C. Greubel_, May 20 2016: (Start)
%F A273366 E.g.f.: 2*(1 + 10*x + 5*x^2)*exp(x).
%F A273366 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). (End)
%F A273366 a(n) = 2*A062786(n+1). - _R. J. Mathar_, Jun 03 2016
%F A273366 Sum_{n>=0} 1/a(n) = Pi/(2*sqrt(5)) * tan(Pi/(2*sqrt(5))) (A350760). - _Amiram Eldar_, Jan 20 2022
%t A273366 LinearRecurrence[{3,-3,1}, {2, 22, 62}, 50] (* _G. C. Greubel_, May 20 2016 *)
%t A273366 Table[10n^2+10n+2,{n,0,40}] (* _Harvey P. Dale_, May 21 2024 *)
%o A273366 (PARI) a(n)=10*n^2+10*n+2 \\ _Charles R Greathouse IV_, Jan 31 2017
%Y A273366 Cf. A062786, A132356, A273365, A273367, A273368, A350760.
%Y A273366 Cf. A033583 (perfect squares ending in 0 in base 10 with final 0 removed).
%K A273366 nonn,easy
%O A273366 0,1
%A A273366 _Nathan Fox_, _Brooke Logan_, and _N. J. A. Sloane_, May 20 2016