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 A140429 #18 Apr 16 2018 11:10:20 %S A140429 0,1,3,9,27,81,243,729,2187,6561,19683,59049,177147,531441,1594323, %T A140429 4782969,14348907,43046721,129140163,387420489,1162261467,3486784401, %U A140429 10460353203,31381059609,94143178827,282429536481,847288609443 %N A140429 a(n) = floor(3^(n-1)). %C A140429 Binomial transform of Jacobsthal numbers A001045. %C A140429 Implicit use in A094555 (Barry). %H A140429 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (3). %F A140429 a(n) = floor(3^(n-1)) = A000244(n-1) = A133494(n), n >= 1. %F A140429 O.g.f.: x/(1-3x). - _R. J. Mathar_, Aug 27 2008 %o A140429 (PARI) a(n)=if(n<2,n,3^(n-1)) \\ _Charles R Greathouse IV_, Oct 03 2016 %o A140429 (PARI) a(n)=floor(3^(n-1)) \\ _M. F. Hasler_, Apr 13 2018 %Y A140429 Cf. A000079, A131577, A133494. %K A140429 nonn,easy %O A140429 0,3 %A A140429 _Paul Curtz_, Jun 19 2008 %E A140429 Extended by _R. J. Mathar_, Aug 28 2008 %E A140429 New name by _M. F. Hasler_, Apr 13 2018