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 A143086 #23 Jun 09 2025 04:41:01
%S A143086 1,1,1,1,3,1,1,3,3,1,1,3,7,3,1,1,3,7,7,3,1,1,3,7,15,7,3,1,1,3,7,15,15,
%T A143086 7,3,1,1,3,7,15,31,15,7,3,1,1,3,7,15,31,31,15,7,3,1,1,3,7,15,31,63,31,
%U A143086 15,7,3,1,1,3,7,15,31,63,63,31,15,7,3,1,1,3,7,15,31,63,127,63,31,15,7,3,1
%N A143086 Triangle read by rows: T(n,k) = 2^(k + 1) - 1 if k < = floor(n/2), otherwise 2^(n - k + 1) - 1, for 0 <= k <= n.
%e A143086 Triangle begins:
%e A143086 {1},
%e A143086 {1, 1},
%e A143086 {1, 3, 1},
%e A143086 {1, 3, 3, 1},
%e A143086 {1, 3, 7, 3, 1},
%e A143086 {1, 3, 7, 7, 3, 1},
%e A143086 {1, 3, 7, 15, 7, 3, 1},
%e A143086 {1, 3, 7, 15, 15, 7, 3, 1},
%e A143086 {1, 3, 7, 15, 31, 15, 7, 3, 1},
%e A143086 {1, 3, 7, 15, 31, 31, 15, 7, 3, 1},
%e A143086 {1, 3, 7, 15, 31, 63, 31, 15, 7, 3, 1}
%t A143086 Table[Table[If[m <= Floor[n/2], 2^(m + 1) - 1, 2^(n - m + 1) - 1], {m, 0, n}], {n, 0, 10}] // Flatten
%Y A143086 Cf. A077866 (row sums).
%K A143086 nonn,tabl,easy,less
%O A143086 0,5
%A A143086 _Roger L. Bagula_ and _Gary W. Adamson_, Oct 16 2008
%E A143086 Offset changed to 0 by _Georg Fischer_, Jun 08 2023