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A318875
Number of divisors d of n for which 2*phi(d) < d.
4
0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2, 0, 1, 0, 0, 0, 2, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 3, 0, 0, 0, 1, 0, 4, 0, 1, 0, 3, 0, 3, 0, 2, 0, 1, 0, 4, 0, 2, 0, 2, 0, 3, 0, 3, 0, 1, 0, 6, 0, 1, 0, 0, 0, 3, 0, 2, 0, 3, 0, 6, 0, 1, 0, 2, 0, 3, 0, 4, 0, 1, 0, 6, 0, 1, 0, 3, 0, 5, 0, 2, 0, 1, 0, 5, 0, 2, 0, 4, 0, 3, 0, 3, 1
OFFSET
1,12
LINKS
FORMULA
a(n) = Sum_{d|n} [A083254(d) < 0].
For all n >= 1, a(n) + A318874(n) + A007814(n) = A000005(n).
MAPLE
A318875 := n -> nops(select(d -> (2*numtheory:-phi(d)) < d, divisors(n))):
seq(A318875(n), n=1..199); # Peter Luschny, Sep 05 2018
MATHEMATICA
A318875[n_] := DivisorSum[n, 1 &, 2*EulerPhi[#] < # &];
Array[A318875, 100] (* Paolo Xausa, Jul 08 2024 *)
PROG
(PARI) A318875(n) = sumdiv(n, d, (2*eulerphi(d))<d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 05 2018
STATUS
approved