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 A013778 #32 Feb 26 2023 14:46:31 %S A013778 3,243,19683,1594323,129140163,10460353203,847288609443, %T A013778 68630377364883,5559060566555523,450283905890997363, %U A013778 36472996377170786403,2954312706550833698643,239299329230617529590083,19383245667680019896796723 %N A013778 a(n) = 3^(4*n + 1). %C A013778 Equivalently, powers of 3 with final digit 3. - _Muniru A Asiru_, Feb 06 2019 %H A013778 Vincenzo Librandi, <a href="/A013778/b013778.txt">Table of n, a(n) for n = 0..200</a> %H A013778 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a> %H A013778 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (81). %F A013778 From _Philippe Deléham_, Nov 25 2008: (Start) %F A013778 a(n) = 81*a(n-1); a(0)=3. %F A013778 G.f.: 3/(1-81*x). (End) %p A013778 seq(coeff(series(3/(1-81*x),x,n+1), x, n), n = 0 .. 15); # _Muniru A Asiru_, Feb 06 2019 %t A013778 3^(1 + 4Range[0, 15]) (* _Harvey P. Dale_, Jan 31 2011 *) %t A013778 NestList[81#&,3,20] (* _Harvey P. Dale_, Feb 26 2023 *) %o A013778 (Magma) [3^(4*n+1): n in [0..20]]; // _Vincenzo Librandi_, Jun 27 2011 %o A013778 (Maxima) makelist(3^(4*n+1),n,0,20); /* _Martin Ettl_, Oct 21 2012 */ %o A013778 (GAP) List([0..15],n->3^(4*n+1)); # _Muniru A Asiru_, Feb 06 2019 %K A013778 nonn,easy %O A013778 0,1 %A A013778 _N. J. A. Sloane_