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 A202149 #9 Mar 30 2012 17:27:26
%S A202149 0,2,1,2,0,0,2,4,3,1,2,4,2,4,2,2,4,1,2,4,1,2,4,0,0,0,0,0,2,4,8,7,5,1,
%T A202149 2,4,2,4,8,6,2,4,8,6,2,2,4,8,5,10,9,7,3,6,1,2,4,8,4,8,4,8,4,8,4,8,2,4,
%U A202149 8,3,6,12,11,9,5,10,7,1,2,4,8,2,4,8,2,4
%N A202149 Triangle read by rows: T(n, k) = mod(2^k, n), where 1 <= k < n.
%C A202149 Rows indexed by odd primes end in 1 (and of course so do rows indexed by base 2 pseudoprimes, A001567). Of those rows, the ones that are permutations of the integers 1 to p - 1 correspond to primes with primitive root 2 (A001122).
%H A202149 T. D. Noe, <a href="/A202149/b202149.txt">Rows n = 2..100, flattened</a>
%e A202149 Triangle starts:
%e A202149 0
%e A202149 2 1
%e A202149 2 0 0
%e A202149 2 4 3 1
%e A202149 2 4 2 4 2
%e A202149 2 4 1 2 4 1
%e A202149 2 4 0 0 0 0 0
%e A202149 2 4 8 7 5 1 2 4
%e A202149 2 4 8 6 2 4 8 6 2
%e A202149 2 4 8 5 10 9 7 3 6 1
%e A202149 2 4 8 4 8 4 8 4 8 4 8
%t A202149 ColumnForm[Table[PowerMod[2, k, n], {n, 2, 20}, {k, n - 1}], Center]
%Y A202149 Cf. A036117, 2^n mod 11; A036118, 2^n mod 13; A201908, irregular triangle of 2^k mod (2n - 1).
%K A202149 nonn,tabl,easy
%O A202149 2,2
%A A202149 _Alonso del Arte_, Dec 12 2011