A070545 - OEIS

%I #13 Apr 30 2022 09:14:54

%S 1,2,3,4,5,5,6,7,8,8,9,9,10,10,10,11,12,12,13,13,14,14,15,15,16,16,17,

%T 17,18,18,19,20,20,20,21,22,23,23,24,24,25,25,26,26,26,26,27,27,28,29,

%U 29,29,30,30,31,31,32,32,33,33,34,34,35,36,37,37,38,38,38,38,39,39,40

%N a(n) = Card( k, 0<k<=n such that k is relatively prime to sigma(k)).

%H Michael De Vlieger, <a href="/A070545/b070545.txt">Table of n, a(n) for n = 1..10000</a>

%t Accumulate[Table[Boole[CoprimeQ[n, DivisorSigma[1, n]]], {n, 1, 100}]] (* _Amiram Eldar_, Apr 30 2022 *)

%o (PARI) for(n=1,100,print1(sum(i=1,n,if(gcd(i, sigma(i))-1,0,1)),","))

%Y Partial sums of A325964.

%Y Cf. A000203, A009194, A014567.

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, May 02 2002