cp's OEIS Frontend

A340087 a(n) = gcd(n-1, A091732(n)), where A091732 is an infinitary analog of Euler's phi function.

%I A340087 #7 Dec 31 2020 08:20:52
%S A340087 1,1,2,3,4,1,6,1,8,1,10,1,12,1,2,15,16,1,18,1,4,1,22,1,24,1,2,9,28,1,
%T A340087 30,1,4,1,2,1,36,1,2,3,40,1,42,1,4,1,46,1,48,1,2,3,52,1,2,1,4,1,58,1,
%U A340087 60,1,2,9,16,5,66,1,4,3,70,1,72,1,2,3,4,1,78,1,80,1,82,1,4,1,2,3,88,1,18,1,4,1,2,5,96
%N A340087 a(n) = gcd(n-1, A091732(n)), where A091732 is an infinitary analog of Euler's phi function.
%H A340087 Antti Karttunen, <a href="/A340087/b340087.txt">Table of n, a(n) for n = 1..65537</a>
%F A340087 a(n) = gcd(n-1, A091732(n)).
%F A340087 a(n) = A091732(n) / A340088(n).
%F A340087 For n > 1, a(n) = (n-1) / A340089(n).
%o A340087 (PARI)
%o A340087 ispow2(n) = (n && !bitand(n,n-1));
%o A340087 A302777(n) = ispow2(isprimepower(n));
%o A340087 A091732(n) = { my(m=1); while(n > 1, fordiv(n, d, if((d<n)&&A302777(n/d), m *= ((n/d)-1); n = d; break))); (m); };
%o A340087 A340087(n) = gcd(n-1, A091732(n));
%Y A340087 Cf. A091732, A340088, A340089.
%Y A340087 Cf. also A049559.
%K A340087 nonn
%O A340087 1,3
%A A340087 _Antti Karttunen_, Dec 31 2020