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 A073477 #19 Aug 24 2025 02:53:12
%S A073477 2,4,8,16,32,12,20,256,44,1024,2048,4096,8192,16384,992,65536,724,
%T A073477 262144,2080,1048576,16256,4194304,8388608,16777216,33554432,67108864,
%U A073477 48832,268435456,536870912,1073741824,471808,4294967296,8589934592,17179869184,34359738368
%N A073477 Least k such that 2^n = k^2-sigma(k)*phi(k).
%C A073477 Sequence is always defined since for s=2^(n+1), 2^n = s^2-sigma(s)*phi(s). - _R. J. Mathar_, Oct 01 2011
%C A073477 a(38) = 67100672. a(50) = 17179738112. a(56) <= 274877382656. - _Donovan Johnson_, Oct 02 2011
%F A073477 a(n) = min{k: A069249(k)=2^n}. - _R. J. Mathar_, Oct 01 2011
%o A073477 (PARI) a(n)=if(n<0,0,x=1; while(abs(x^2-sigma(x)*eulerphi(x)-2^n)>0,x++)); x
%K A073477 nonn,changed
%O A073477 0,1
%A A073477 _Benoit Cloitre_, Aug 26 2002
%E A073477 Edited and extended by _Klaus Brockhaus_, Aug 29 2002
%E A073477 a(26) and a(30) from _R. J. Mathar_, Oct 01 2011
%E A073477 a(25), a(27)-a(29) and a(31)-a(34) from _Donovan Johnson_, Oct 02 2011