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 A355482 #12 Jul 04 2022 20:49:20 %S A355482 2,4,3,8,7,16,15,11,32,31,64,63,47,128,127,256,255,191,512,511,13, %T A355482 1024,1023,223,2048,2047,14,19,4096,4095,8388607,21,22,25,5,8192,8191, %U A355482 16384,16383,239,32768,32767,247,26,28,55,35,37,65536,65535,49151,38,41,131072,131071,262144,262143 %N A355482 a(1) = 2; for n > 1, a(n) is the smallest positive number that has not yet appeared such that the number of 1-bits in the binary expansion of a(n) equals the number of proper divisors of a(n-1). %C A355482 This sequence is similar to A355374 but the rules for determining a(n) are reversed. The only fixed point in the first 145 terms is a(3) = 3. It is unknown if all numbers eventually appear. The last known term is a(145) which is a 154 digit number whose complete factorization is unknown. %H A355482 Scott R. Shannon, <a href="/A355482/b355482.txt">Table of n, a(n) for n = 1..145</a> %e A355482 a(7) = 15 = 1111_2 as a(6) = 16 which has four proper divisors, and 15 is the smallest unused number that has four 1-bits in its binary expansion. %Y A355482 Cf. A355483 (all divisors), A355374, A000120, A032741, A005179, A027751. %K A355482 nonn,base %O A355482 1,1 %A A355482 _Scott R. Shannon_, Jul 03 2022