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 A129142 #3 Sep 08 2022 08:45:30 %S A129142 1,3,4,7,8,9,15,16,17,18,31,32,33,34,35,63,64,65,66,67,68,127,128,129, %T A129142 130,131,132,133,255,256,257,258,259,260,261,262,511,512,513,514,515, %U A129142 516,517,518,519,1023,1024,1025,1026,1027,1028,1029,1030,1031,1032,2047 %N A129142 Start with the empty sequence and append in step k the consecutive numbers 2^k-1 to 2^k+k-2. %C A129142 Inspired by A127330. %e A129142 In step 4 the numbers 2^4-1 to 2^4+4-2 are appended: 15, 16, 17, 18. %o A129142 (Magma) &cat[ [2^k-1..2^k+k-2]: k in [1..11] ]; %Y A129142 Cf. A127330, A129143. %K A129142 nonn,easy %O A129142 1,2 %A A129142 _Klaus Brockhaus_, Mar 31 2007