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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))

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