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A092588 Numbers k such that sigma(phi(k)) - phi(sigma(k)) is nonzero and divisible by sigma(k), that is A065395(k)/A000203(k) is a nonzero integer. 6
7, 327, 463, 497, 617, 691, 751, 1207, 1633, 2451, 2643, 3143, 3337, 3503, 4939, 5609, 7093, 7597, 10327, 14987, 20427, 21103, 22345, 22481, 24739, 26491, 27193, 28077, 37753, 37915, 42711, 42717, 47647, 48043, 49243, 50071, 51727, 54823, 57478 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

(sigma(phi(x))-phi(sigma(x)))/sigma(x) quotient equals 1 for x=7, 2 for x=327, 3 for x=5609.

MATHEMATICA

fs[x_] := EulerPhi[DivisorSigma[1, x]] sf[x_] := DivisorSigma[1, EulerPhi[x]] {t=Table[0, {100}], j=1}; Do[s=(sf[n]-fs[n])/DivisorSigma[1, n]; If[ !Equal[s, 0]&&IntegerQ[s], Print[n]; t[[j]]=n; j=j+1], {n, 2, 1000000}] t

PROG

(PARI) is(n)=my(s=sigma(n), t=sigma(eulerphi(n))-eulerphi(s)); t && t%s==0 \\ Charles R Greathouse IV, Feb 14 2013

CROSSREFS

Cf. A000010, A000203, A033632, A065395, A092584-A092588.

Sequence in context: A163437 A109059 A002000 * A049686 A177019 A160432

Adjacent sequences:  A092585 A092586 A092587 * A092589 A092590 A092591

KEYWORD

nonn

AUTHOR

Labos Elemer, Mar 01 2004

STATUS

approved

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Last modified July 10 15:45 EDT 2020. Contains 335577 sequences. (Running on oeis4.)