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 A345305 #9 Jan 24 2025 09:42:00
%S A345305 0,1,1,4,1,5,1,8,9,7,1,16,1,9,8,16,1,27,1,24,10,13,1,32,25,15,27,32,1,
%T A345305 31,1,32,14,19,12,72,1,21,16,48,1,41,1,48,54,25,1,64,49,75,20,56,1,81,
%U A345305 16,64,22,31,1,92,1,33,72,64,18,61,1,72,26,59,1,144,1,39,100,80,18
%N A345305 a(n) = n * Sum_{p|n, p prime} gcd(p,n/p) / p.
%C A345305 If p is prime, a(p) = p * Sum_{p|p} gcd(p,p/p) / p = p * (1/p) = 1.
%H A345305 Antti Karttunen, <a href="/A345305/b345305.txt">Table of n, a(n) for n = 1..20000</a>
%e A345305 a(18) = 18 * Sum_{p|18} gcd(p,18/p) / p = 18 * (gcd(2,9)/2 + gcd(3,6)/3) = 18 * (1/2 + 1) = 27.
%t A345305 Table[n*Sum[(1/k) GCD[k, n/k] (PrimePi[k] - PrimePi[k - 1]) (1 - Ceiling[n/k] + Floor[n/k]), {k, n}], {n, 100}]
%o A345305 (PARI) A345305(n) = if(1==n, 0, my(f=factor(n)); n*sum(i=1, #f~, (gcd(f[i,1],n/f[i, 1])/f[i,1]))); \\ _Antti Karttunen_, Jan 24 2025
%Y A345305 Cf. A345266.
%K A345305 nonn
%O A345305 1,4
%A A345305 _Wesley Ivan Hurt_, Jun 13 2021