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 A009205 #25 Jan 31 2025 03:55:05
%S A009205 1,1,2,1,2,4,2,1,1,2,2,2,2,4,4,1,2,3,2,6,4,4,2,4,1,2,4,2,2,8,2,3,4,2,
%T A009205 4,1,2,4,4,2,2,8,2,6,6,4,2,2,3,3,4,2,2,8,4,8,4,2,2,12,2,4,2,1,4,8,2,6,
%U A009205 4,8,2,3,2,2,2,2,4,8,2,2,1,2,2,4,4,4,4,4,2,6,4,6,4,4,4,12,2,3,6,1,2,8,2,2,8,2,2,4,2,8,4,2,2,8,4,6,2,4,4,8
%N A009205 a(n) = gcd(d(n), sigma(n)).
%H A009205 Antti Karttunen, <a href="/A009205/b009205.txt">Table of n, a(n) for n = 1..10000</a>
%F A009205 a(n) = A064840(n)/A009278(n). - _Amiram Eldar_, Jan 31 2025
%t A009205 Table[GCD[DivisorSigma[0,n],DivisorSigma[1,n]],{n,120}] (* _Harvey P. Dale_, Dec 05 2017 *)
%o A009205 (PARI) A009205(n) = gcd(numdiv(n),sigma(n)); \\ _Antti Karttunen_, May 22 2017
%o A009205 (Python)
%o A009205 from math import prod, gcd
%o A009205 from sympy import factorint
%o A009205 def A009205(n):
%o A009205 f = factorint(n).items()
%o A009205 return gcd(prod(e+1 for p, e in f),prod((p**(e+1)-1)//(p-1) for p,e in f)) # _Chai Wah Wu_, Jul 27 2023
%Y A009205 Cf. A000005, A000203, A009191, A009194, A009278, A064840, A087801, A286360.
%K A009205 nonn
%O A009205 1,3
%A A009205 _David W. Wilson_
%E A009205 Data section extended to 120 terms by _Antti Karttunen_, May 22 2017