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 A227984 #20 Sep 08 2022 08:46:05
%S A227984 1,3,1,7,1,1,15,7,3,1,31,5,1,1,1,63,31,15,7,3,1,127,21,31,1,7,1,1,255,
%T A227984 127,9,31,15,1,3,1,511,85,127,21,1,5,7,1,1,1023,511,255,127,63,31,15,
%U A227984 7,3,1,2047,341,73,17,127,1,31,1,1,1,1,4095,2047,1023
%N A227984 Triangle T(n,k), read by rows: T(n,k) is the numerator of (1-2^(n-k+1))/(1-2^(k+1)).
%C A227984 The denominators are given in A228035.
%C A227984 The first column is A000225, the second column is A213243, and the third column is A213245.
%H A227984 Vincenzo Librandi, <a href="/A227984/b227984.txt">Rows n = 0..100, flattened</a>
%e A227984 Triangle begins:
%e A227984 1;
%e A227984 3, 1;
%e A227984 7, 1, 1;
%e A227984 15, 7, 3, 1;
%e A227984 31, 5, 1, 1, 1;
%e A227984 63, 31, 15, 7, 3, 1;
%e A227984 127, 21, 31, 1, 7, 1, 1;
%e A227984 255, 127, 9, 31, 15, 1, 3, 1;
%e A227984 511, 85, 127, 21, 1, 5, 7, 1, 1;
%e A227984 1023, 511, 255, 127, 63, 31, 15, 7, 3, 1;
%e A227984 2047, 341, 73, 17, 127, 1, 31, 1, 1, 1, 1; etc.
%t A227984 a[n_, k_] := Numerator[(1 - 2^(n - k + 1))/(1 - 2^(k + 1))];
%t A227984 Table[a[n, k], {n, 0, 11}, {k, 0, n}] // Flatten
%o A227984 (Magma) [Numerator((1-2^(n-k+1))/(1-2^(k+1))): k in [0..n], n in [0..11]];
%Y A227984 Cf. A000225, A213243, A213245, A228035.
%K A227984 nonn,tabl,frac
%O A227984 0,2
%A A227984 _Vincenzo Librandi_, Aug 12 2013