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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,12

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

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

PROG

(PARI) A318875(n) = sumdiv(n, d, (2*eulerphi(d))<d);

CROSSREFS

Cf. A000010, A083254, A318874, A318877, A318879.

Sequence in context: A265245 A110270 A284825 * A187143 A187144 A123635

Adjacent sequences:  A318872 A318873 A318874 * A318876 A318877 A318878

KEYWORD

nonn

AUTHOR

Antti Karttunen, Sep 05 2018

STATUS

approved

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Last modified June 22 16:23 EDT 2021. Contains 345386 sequences. (Running on oeis4.)