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 A290781 #19 Apr 12 2025 11:34:12 %S A290781 15,35,55,75,95,115,135,155,175,195,215,235,255,275,295,315,335,355, %T A290781 375,395,415,435,455,475,495,515,535,555,575,595,615,635,655,675,695, %U A290781 715,735,755,775,795,815,835,855,875,895,915,935,955,975,995,1015,1035 %N A290781 a(n) = 20*n + 15. %C A290781 Bisection of A017329. %C A290781 None of the numbers in this sequence is a Fermat pseudoprime to base 2. %H A290781 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1). %F A290781 G.f.: 5*(3 + x)/(1 - x)^2. %F A290781 a(n) = A004767(A016885(n)) = A004767(A004767(n) + n). - _Torlach Rush_, Oct 10 2019 %F A290781 E.g.f.: 5*exp(x)*(3 + 4*x). - _Stefano Spezia_, Oct 12 2019 %F A290781 From _Elmo R. Oliveira_, Apr 12 2025: (Start) %F A290781 a(n) = 5*A004767(n) = A017329(2*n+1) = A008587(4*n+3). %F A290781 a(n) = 2*a(n-1) - a(n-2). (End) %t A290781 Range[15, 1035, 20] %o A290781 (Magma) [n: n in [15..1035 by 20]]; %Y A290781 Cf. A001567, A004767, A008587, A016885, A017329. %K A290781 nonn,easy %O A290781 0,1 %A A290781 _Arkadiusz Wesolowski_, Aug 10 2017