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 A174371 #39 Aug 19 2023 19:45:48
%S A174371 1,25,121,289,529,841,1225,1681,2209,2809,3481,4225,5041,5929,6889,
%T A174371 7921,9025,10201,11449,12769,14161,15625,17161,18769,20449,22201,
%U A174371 24025,25921,27889,29929,32041,34225,36481,38809,41209,43681,46225,48841,51529
%N A174371 a(n) = (6*n-1)^2.
%C A174371 Unit together with numbers of form (6*n+5)^2.
%C A174371 Sequence may be obtained by starting with the segment (1, 25) followed by the line from 25 in the direction 25, 121,... in the square spiral whose vertices are the generalized 20-gonal numbers. - _Omar E. Pol_, Jul 29 2016
%H A174371 Vincenzo Librandi, <a href="/A174371/b174371.txt">Table of n, a(n) for n = 0..1000</a>
%H A174371 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A174371 a(n) = A016970(n-1), n >= 1.
%F A174371 G.f.: (49*x^2 + 22*x + 1)/(1 - x)^3. - _Vincenzo Librandi_, Jan 27 2013
%F A174371 a(n) = 6*A033579(n) + 1. - _Miquel Cerda_, Jul 28 2016
%F A174371 a(n) = 36n^2 - 12n + 1. - _Omar E. Pol_, Jul 28 2016
%F A174371 E.g.f.: exp(x)*(1 + 24*x + 36*x^2). - _Stefano Spezia_, Aug 19 2023
%e A174371 a(0)=1 because (6*0-1)^2=1, a(1)=25 because (6*1-1)^2=25.
%t A174371 CoefficientList[Series[(49*x^2 + 22*x + 1)/(1 - x)^3, {x, 0, 40}], x] (* _Vincenzo Librandi_, Jan 27 2013 *)
%o A174371 (Magma) [(6*n-1)^2: n in [0..50]]; // _Vincenzo Librandi_, May 07 2011
%o A174371 (PARI) a(n)=(6*n-1)^2 \\ _Charles R Greathouse IV_, Jul 28 2016
%Y A174371 Cf. A016970, A033579.
%K A174371 nonn,easy
%O A174371 0,2
%A A174371 _Juri-Stepan Gerasimov_, Mar 17 2010
%E A174371 Offset and formula corrected by _R. J. Mathar_, Apr 16 2010