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 A099973 #14 Aug 02 2025 20:24:34
%S A099973 1,9,73,201,457,969,9161,140233,402377,2499529,6693833,15082441,
%T A099973 31859657,65414089,132522953,1206264777,3353748425,11943683017,
%U A099973 29123552201,63483290569,132202767305,269641720777,819397534665
%N A099973 Write Euler's constant gamma as a binary fraction; read this from left to right and whenever a 1 appears, note the integer formed by reading leftwards from that 1.
%e A099973 gamma = 0.577215664901532860606512090082402431042159335939923598805... = 0.1001001111000100011001111110001101111101101100001100011110100100110100011011... in binary.
%t A099973 d = 100; l = First[RealDigits[N[EulerGamma, d], 2]]; Do[m = Take[l, n]; k = Length[m]; If[m[[k]] == 1, Print[FromDigits[Reverse[m], 2]]], {n, 1, d}] (* _Ryan Propper_, Aug 18 2005 *)
%Y A099973 Cf. A001620, A099969, A099970, A099971, A099972, A099974.
%K A099973 nonn,easy
%O A099973 0,2
%A A099973 _N. J. A. Sloane_, Nov 13 2004, based on correspondence from _Artur Jasinski_, Mar 25 2003
%E A099973 More terms from _Ryan Propper_, Aug 18 2005