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 A113870 #15 Jul 08 2024 21:33:54 %S A113870 1,3,7,39,103,615,1639,9831,26215,157287,419431,2516583,6710887, %T A113870 40265319,107374183,644245095,1717986919,10307921511,27487790695, %U A113870 164926744167,439804651111,2638827906663,7036874417767,42221246506599 %N A113870 a(n) = a(n-1) + 2^(k(n)), where k(n) is the n-th term of the sequence formed by k(1)=0 together with the numbers A042963. %H A113870 Vincenzo Librandi, <a href="/A113870/b113870.txt">Table of n, a(n) for n = 1..300</a> %H A113870 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1, 16, -16). %F A113870 G.f.: (3+x-40*x^2)/(4*(-1+x)*(-1+4*x)*(1+4*x)). - _Vaclav Kotesovec_, Nov 28 2012 %o A113870 (PARI) a(n)=([0,1,0; 0,0,1; -16,16,1]^(n-1)*[1;3;7])[1,1] \\ _Charles R Greathouse IV_, Jul 08 2024 %Y A113870 Cf. A099974, A112627, A080355, A080567, A099969, A099970, A099971. %K A113870 nonn,easy %O A113870 1,2 %A A113870 _Artur Jasinski_, Jan 27 2006 %E A113870 Edited with better definition and offset corrected by _Omar E. Pol_, Jan 08 2009