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 A156605 #20 Jun 15 2023 11:33:53 %S A156605 7,8,12,28,92,348,1372,5468,21852,87388,349532,1398108,5592412, %T A156605 22369628,89478492,357913948,1431655772,5726623068,22906492252, %U A156605 91625968988,366503875932,1466015503708,5864062014812,23456248059228,93824992236892,375299968947548 %N A156605 a(n) = (4^n + 20)/3. %H A156605 Vincenzo Librandi, <a href="/A156605/b156605.txt">Table of n, a(n) for n = 0..1000</a> %H A156605 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (5, -4). %F A156605 a(n) = -A156591(2n+1). %F A156605 a(n) = 4 + A154879(2n) = 7 + A002450(n). %F A156605 a(n) = 4*a(n-1) - 20, n > 0. %F A156605 G.f.: (7 - 27*x)/((1-x)*(1-4*x)). - _R. J. Mathar_, Feb 23 2009 %F A156605 E.g.f.: (1/3)*(20*exp(x) + exp(4*x)). - _G. C. Greubel_, Jun 25 2021 %t A156605 (4^Range[0,40] + 20)/3 (* _G. C. Greubel_, Jun 25 2021 *) %o A156605 (Magma) [(4^n+20)/3: n in [0..35]]; // _Vincenzo Librandi_, Jul 24 2011 %o A156605 (Sage) [(4^n + 20)/3 for n in (0..40)] # _G. C. Greubel_, Jun 25 2021 %Y A156605 Cf. A002450, A154879, A156591. %K A156605 nonn,easy %O A156605 0,1 %A A156605 _Paul Curtz_, Feb 11 2009 %E A156605 Edited and extended by _R. J. Mathar_, Feb 23 2009