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 A241850 #27 Nov 29 2024 19:05:22
%S A241850 20,21,24,29,36,45,56,69,84,101,120,141,164,189,216,245,276,309,344,
%T A241850 381,420,461,504,549,596,645,696,749,804,861,920,981,1044,1109,1176,
%U A241850 1245,1316,1389,1464,1541,1620,1701,1784,1869,1956,2045,2136,2229,2324,2421,2520
%N A241850 a(n) = n^2 + 20.
%C A241850 The only solution for x at the Diophantine equation x^2 + 20 = y^m (with m > 2) is 14: 14^2 + 20 = a(14) = 6^3. - _Bruno Berselli_, May 01 2014
%H A241850 Vincenzo Librandi, <a href="/A241850/b241850.txt">Table of n, a(n) for n = 0..1000</a>
%H A241850 J. H. E. Cohn, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa65/aa6546.pdf">The diophantine equation x^2 + C = y^n</a>, Acta Arithmetica LXV.4, 1993, p. 379.
%H A241850 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A241850 G.f.: (20 - 39*x + 21*x^2)/(1 - x)^3.
%F A241850 a(n) = a(-n) = 3*a(n-1) - 3*a(n-2) + a(n-3) = a(n-1) + 2*n - 1.
%F A241850 From _Amiram Eldar_, Nov 03 2020: (Start)
%F A241850 Sum_{n>=0} 1/a(n) = (1 + sqrt(20)*Pi*coth(sqrt(20)*Pi))/40.
%F A241850 Sum_{n>=0} (-1)^n/a(n) = (1 + sqrt(20)*Pi*cosech(sqrt(20)*Pi))/40. (End)
%F A241850 E.g.f.: exp(x)*(20 + x + x^2). - _Elmo R. Oliveira_, Nov 29 2024
%t A241850 Table[n^2 + 20, {n, 0, 60}]
%o A241850 (Magma) [n^2+20: n in [0..60]];
%o A241850 (PARI) a(n)=n^2+20 \\ _Charles R Greathouse IV_, Jun 17 2017
%Y A241850 Cf. similar sequences listed in A114962.
%K A241850 nonn,easy
%O A241850 0,1
%A A241850 _Vincenzo Librandi_, May 01 2014