A129139 - OEIS

%I #13 Apr 01 2021 14:45:05

%S 1,1,2,2,2,1,2,2,2,2,2,2,2,2,3,3,2,2,2,2,3,2,2,3,3,2,3,3,2,2,2,3,3,2,

%T 4,3,2,2,3,3,2,2,2,3,3,2,2,3,3,2,3,3,2,3,4,3,3,2,2,3,2,2,4,4,4,3,2,3,

%U 3,2,2,4,2,2,3,3,4,3,2,4,4,2,2,3,4,2,3,4,2,3,4,3,3,2,4,4,2,3,4,4,2,3,2,4,4

%N a(n) = number of positive integers which are coprime to n and are <= d(n), where d(n) = A000005(n).

%H Antti Karttunen, <a href="/A129139/b129139.txt">Table of n, a(n) for n = 1..16384</a>

%e d(16) = 5. So a(16) is the number of integers coprime to 16 which are <= 5. There are 3 such integers: 1, 3, 5; so a(16) = 3.

%p with(numtheory): a:=proc(n) local ct,j: ct:=0: for j from 1 to tau(n) do if gcd(j,n)=1 then ct:=ct+1 else fi od: ct; end: seq(a(n),n=1..140); # _Emeric Deutsch_, Apr 02 2007

%o (PARI) A129139(n) = sum(k=1,numdiv(n),(1==gcd(k,n))); \\ _Antti Karttunen_, Apr 01 2021

%Y Cf. A000005, A129138, A126131, A074919.

%K nonn

%O 1,3

%A _Leroy Quet_, Mar 30 2007

%E More terms from _Emeric Deutsch_, Apr 02 2007