A318877 - OEIS

%I #16 Jul 08 2024 11:57:37

%S 0,0,0,0,0,6,0,0,0,10,0,18,0,14,0,0,0,24,0,30,0,22,0,42,0,26,0,42,0,

%T 46,0,0,0,34,0,72,0,38,0,70,0,62,0,66,0,46,0,90,0,60,0,78,0,78,0,98,0,

%U 58,0,138,0,62,0,0,0,94,0,102,0,94,0,168,0,74,0,114,0,110,0,150,0,82,0,186,0,86,0,154,0,154,0,138,0,94,0

%N Sum of divisors d of n for which 2*phi(d) < d.

%H Antti Karttunen, <a href="/A318877/b318877.txt">Table of n, a(n) for n = 1..65537</a>

%H <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>

%F a(n) = Sum_{d|n} [2*phi(d) < d]*d, where [ ] are the Iverson brackets.

%F For all n >= 1, a(n) + A318876(n) + 2*(A006519(n)-1) = A000203(n).

%t A318877[n_] := DivisorSum[n,  # &, 2*EulerPhi[#] < # &];

%t Array[A318877, 100] (* _Paolo Xausa_, Jul 08 2024 *)

%o (PARI) A318877(n) = sumdiv(n,d,((2*eulerphi(d))<d)*d);

%Y Cf. A000010, A000203, A006519, A083254, A318875, A318876, A318879.

%Y Cf. also A187795.

%K nonn

%O 1,6

%A _Antti Karttunen_, Sep 05 2018