cp's OEIS Frontend

A340080 a(n) = (1+A018804(n)) / gcd(n, 1+A018804(n)), where A018804(n) = Sum_{k=1..n} gcd(k, n).

%I A340080 #7 Dec 31 2020 08:20:45
%S A340080 2,2,2,9,2,8,2,21,22,14,2,41,2,20,46,49,2,32,2,73,22,32,2,101,66,38,
%T A340080 82,15,2,68,2,113,106,50,118,169,2,56,42,181,2,14,2,169,38,68,2,241,
%U A340080 134,98,166,201,2,122,38,261,62,86,2,361,2,92,274,257,226,158,2,265,226,176,2,421,2,110,326,297,274,188
%N A340080 a(n) = (1+A018804(n)) / gcd(n, 1+A018804(n)), where A018804(n) = Sum_{k=1..n} gcd(k, n).
%H A340080 Antti Karttunen, <a href="/A340080/b340080.txt">Table of n, a(n) for n = 1..8191</a>
%H A340080 Antti Karttunen, <a href="/A340080/a340080.txt">Data supplement: n, a(n) computed for n = 1..65537</a>
%F A340080 a(n) = (1+A018804(n)) / gcd(n, 1+A018804(n)).
%o A340080 (PARI)
%o A340080 A018804(n) = sumdiv(n, d, n*eulerphi(d)/d); \\ From A018804
%o A340080 A340080(n) = { my(x=1+A018804(n)); x/gcd(n,x); };
%Y A340080 Cf. A018804, A340078, A340079.
%K A340080 nonn
%O A340080 1,1
%A A340080 _Antti Karttunen_, Dec 31 2020