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 A098355 #13 Aug 03 2014 14:37:23
%S A098355 1,3,3,9,9,9,27,27,27,27,81,81,81,81,81,243,243,243,243,243,243,729,
%T A098355 729,729,729,729,729,729,2187,2187,2187,2187,2187,2187,2187,2187,6561,
%U A098355 6561,6561,6561,6561,6561,6561,6561,6561,19683,19683,19683,19683,19683,19683
%N A098355 Multiplication table of the powers of three read by antidiagonals.
%C A098355 3^A003056: 3^n appears n+1 times.
%H A098355 Jeremy Gardiner, <a href="/A098355/b098355.txt">Table of n, a(n) for n = 0..349</a>
%e A098355 1; 3,3; 9,9,9; 27,27,27,27;
%t A098355 Flatten[Table[3^x, {x, 0, 13}, {y, 0, x}]] (* _Alonso del Arte_, Nov 29 2011 *)
%Y A098355 Cf. A000244, A003056, A003991, A098354, A137688.
%K A098355 nonn,tabl
%O A098355 0,2
%A A098355 Douglas Stones (dssto1(AT)student.monash.edu.au), Sep 04 2004