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 A101440 #5 Jul 05 2022 11:42:05 %S A101440 1,2,4,8,16,32,64,128,256,512,5,10,20,40,80,160,320,640,1280,2560,9, %T A101440 18,36,72,144,288,576,1152,2304,4608,17,34,68,136,272,544,1088,2176, %U A101440 4352,8704,33,66,132,264,528,1056,2112,4224,8448,16896,65,130,260,520,1040 %N A101440 Replace each digit of n with 1 followed by n 0's: 0 -> 1, 1 -> 10, 2 -> 100, ..., 9 -> 1000000000, 10 -> 101, 11 -> 1010, 12 -> 10100, etc. Expanded number is then converted from binary to decimal: 0 -> 1 -> 1, 1 -> 10 -> 2, 2 -> 100 -> 4, 9 -> 1000000000 -> 512, 10 -> 101 -> 5, etc. %e A101440 a(123) = 328 : 123 -> 101001000 -> 328. %K A101440 base,easy,nonn %O A101440 0,2 %A A101440 _Felix Tubiana_, Jan 18 2005