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 A140659 #12 Sep 08 2019 12:20:53 %S A140659 0,0,1,2,6,12,25,50,102,204,409,818,1638,3276,6553,13106,26214,52428, %T A140659 104857,209714,419430,838860,1677721,3355442,6710886,13421772, %U A140659 26843545,53687090,107374182,214748364,429496729,858993458,1717986918,3435973836 %N A140659 a(n) = floor(A140657(n+2)/10). %H A140659 Michel Marcus, <a href="/A140659/b140659.txt">Table of n, a(n) for n = 0..100</a> %F A140659 a(2n+2) = 4*a(2n)+A000034(n). %F A140659 a(2n+1) = 2*a(2n). %t A140659 a[ n_] := If[n < 2, 0, 2 a[n - 1] + If[ EvenQ[n], Mod[n/2, 2, 1], 0]]; (* _Michael Somos_, Mar 02 2014 *) %o A140659 (PARI) f(n) = 2^n+3*(-1)^n; \\ A140657 %o A140659 a(n) = f(n+2)\10; \\ _Michel Marcus_, Sep 08 2019 %Y A140659 Cf. A093387. %K A140659 nonn %O A140659 0,4 %A A140659 _Paul Curtz_, Jul 10 2008 %E A140659 Edited and extended by _R. J. Mathar_, Jul 29 2008 %E A140659 Name corrected by _Michel Marcus_, Sep 08 2019