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 A172148 #12 Jul 22 2025 07:32:41
%S A172148 1,2,2,4,4,8,8,14,14,28,28,56,56,112,112,192,192,384,384,768,768,1536,
%T A172148 1536,2688,2688,5376,5376,10752,10752,21504,21504,37632,37632,75264,
%U A172148 75264,150528,150528,301056,301056,526848,526848,1053696,1053696,2107392,2107392
%N A172148 Number of subsets S of {1,2,3,...,n} with the property that if x is a member of S then at least one of x/2 and 2x is also a member of S.
%C A172148 For the terms a(1) through a(25) is it seen that if n is odd then a(n)=a(n-1); also that if n is not a multiple of 4 then a(2n)=2a(2n-2). Does this behavior continue?
%H A172148 David A. Corneth, <a href="/A172148/b172148.txt">Table of n, a(n) for n = 1..6993</a> (terms < 10^1000)
%Y A172148 Cf. A172020.
%K A172148 nonn
%O A172148 1,2
%A A172148 _John W. Layman_, Jan 26 2010
%E A172148 a(26)-a(45) from _Fausto A. C. Cariboni_, Oct 03 2020