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 A201909 #17 Feb 02 2019 03:16:29
%S A201909 1,0,1,3,4,2,1,3,2,6,4,5,1,3,9,5,4,1,3,9,1,3,9,10,13,5,15,11,16,14,8,
%T A201909 7,4,12,2,6,1,3,9,8,5,15,7,2,6,18,16,10,11,14,4,12,17,13,1,3,9,4,12,
%U A201909 13,16,2,6,18,8,1,3,9,27,23,11,4,12,7,21,5,15
%N A201909 Irregular triangle of 3^k mod prime(n).
%C A201909 The row lengths are in A062117. Except for the second row, the first term of each row is 1. Many sequences are in this one: starting at A036119 (mod 17) and A070341 (mod 11).
%H A201909 T. D. Noe, <a href="/A201909/b201909.txt">Rows n = 1..60. flattened</a>
%e A201909 The first 9 rows are:
%e A201909 1
%e A201909 0
%e A201909 1, 3, 4, 2
%e A201909 1, 3, 2, 6, 4, 5
%e A201909 1, 3, 9, 5, 4
%e A201909 1, 3, 9
%e A201909 1, 3, 9, 10, 13, 5, 15, 11, 16, 14, 8, 7, 4, 12, 2, 6
%e A201909 1, 3, 9, 8, 5, 15, 7, 2, 6, 18, 16, 10, 11, 14, 4, 12, 17, 13
%e A201909 1, 3, 9, 4, 12, 13, 16, 2, 6, 18, 8
%t A201909 nn = 10; p = 3; t = p^Range[0,Prime[nn]]; Flatten[Table[If[Mod[n, p] == 0, {0}, tm = Mod[t, n]; len = Position[tm, 1, 1, 2][[-1,1]]; Take[tm, len-1]], {n, Prime[Range[nn]]}]]
%o A201909 (GAP) P:=Filtered([1..350],IsPrime);;
%o A201909 R:=List([1..Length(P)],n->OrderMod(7,P[n]));;
%o A201909 Flat(Concatenation([1,1,1,2,4,3,0],List([5..10],n->List([0..R[n]-1],k->PowerMod(7,k,P[n]))))); # _Muniru A Asiru_, Feb 01 2019
%Y A201909 Cf. A062117, A201908 (2^k), A201910 (5^k), A201911 (7^k).
%Y A201909 Cf. A070352 (5), A033940 (7), A070341 (11), A168399 (13), A036119 (17), A070342 (19), A070356 (23), A070344 (29), A036123 (31), A070346 (37), A070361 (41), A036126 (43), A070364 (47), A036134 (79), A036136 (89), A036142 (113), A036143 (127), A036145 (137), A036158 (199), A036160 (223).
%K A201909 nonn,tabf
%O A201909 1,4
%A A201909 _T. D. Noe_, Dec 07 2011