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 A277046 #55 Nov 27 2021 12:37:04 %S A277046 1,2,3,4,5,6,7,8,9,12,13,14,15,16,17,18,27,28,29,30,31,32,33,34,35,58, %T A277046 59,60,61,62,63,64,65,66,67,68,121,122,123,124,125,126,127,128,129, %U A277046 130,131,132,133,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,503,504,505,506,507,508,509,510,511,512,513,514,515,516,517,518,519 %N A277046 Triangle read by rows: T(n,k) = 2^n - n + k - 1 for n >= 1, with 1 <= k <= 2n-1. %H A277046 Harvey P. Dale, <a href="/A277046/b277046.txt">Table of n, a(n) for n = 1..1000</a> %e A277046 Triangle begins: %e A277046 1; %e A277046 2, 3, 4; %e A277046 5, 6, 7, 8, 9; %e A277046 12, 13, 14, 15, 16, 17, 18; %e A277046 27, 28, 29, 30, 31, 32, 33, 34, 35; %e A277046 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68; %e A277046 ... %e A277046 Written as an isosceles triangle the sequence begins: %e A277046 . 1; %e A277046 . 2, 3, 4; %e A277046 . 5, 6, 7, 8, 9; %e A277046 . 12, 13, 14, 15, 16, 17, 18; %e A277046 . 27, 28, 29, 30, 31, 32, 33, 34, 35; %e A277046 . 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68; %e A277046 .. %t A277046 Table[2^n-n+k-1,{n,10},{k,2n-1}]//Flatten (* _Harvey P. Dale_, Nov 27 2021 *) %Y A277046 Row lengths are A005408. %Y A277046 Row sums give A118414. %Y A277046 Column 1 gives A000325, n>=1. %Y A277046 Middle diagonal gives A000225. %Y A277046 Right border gives A083706. %Y A277046 Cf. A118413. %K A277046 nonn,tabf %O A277046 1,2 %A A277046 _Miquel Cerda_, Sep 27 2016 %E A277046 Definition from _Omar E. Pol_, Sep 28 2016