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 A250024 #28 Apr 04 2025 07:49:35
%S A250024 19,59,99,139,179,219,259,299,339,379,419,459,499,539,579,619,659,699,
%T A250024 739,779,819,859,899,939,979,1019,1059,1099,1139,1179,1219,1259,1299,
%U A250024 1339,1379,1419,1459,1499,1539,1579,1619,1659,1699,1739,1779,1819,1859,1899
%N A250024 a(n) = 40*n - 21.
%C A250024 This is the sequence of numbers congruent to 19 mod 40.
%H A250024 Karl V. Keller, Jr., <a href="/A250024/b250024.txt">Table of n, a(n) for n = 1..10000</a>
%H A250024 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.
%H A250024 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A250024 From _Vincenzo Librandi_, Nov 11 2014: (Start)
%F A250024 G.f.: x*(19+21*x)/(1-x)^2.
%F A250024 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). (End)
%F A250024 From _Elmo R. Oliveira_, Apr 04 2025: (Start)
%F A250024 E.g.f.: 21 + exp(x)*(40*x - 21).
%F A250024 a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)
%t A250024 40 Range[40] - 21 (* _Alonso del Arte_, Nov 10 2014 *)
%t A250024 CoefficientList[Series[(19 + 21 x) / (1 - x)^2, {x, 0, 50}], x] (* _Vincenzo Librandi_, Nov 11 2014 *)
%o A250024 (Python) for n in range(1,101): print(40*n-21,end=",")
%o A250024 (Magma) [40*n-21: n in [1..60]]; // _Vincenzo Librandi_, Nov 11 2014
%o A250024 (PARI) a(n)=40*n-21 \\ _Charles R Greathouse IV_, May 23 2019
%Y A250024 Cf. A017377 (10*n+9), A142190 (prime terms).
%K A250024 nonn,easy
%O A250024 1,1
%A A250024 _Karl V. Keller, Jr._, Nov 10 2014