A092586 Numbers n such that sigma(phi(n))-phi(sigma(n)) is nonzero and is divisible by (n+1), that is A065395(n)/(n+1) = (phi(sigma(n))-sigma(phi(n)))/(n+1) is a nonzero integer.

7, 87, 231, 463, 617, 691, 751, 855, 1059, 1127, 2795, 4819, 11999, 18527, 22481, 75311, 121939, 232901, 256751, 288883, 313919, 371519, 845831, 1285841, 1762799, 1815167, 7195199, 9096191, 40324121, 93070943, 99388823, 113140151, 238072223, 487394063

Offset

1,1

Links

Table of n, a(n) for n=1..34.

Example

(sigma(phi(x))-phi(sigma(x)))/(x+1) equals 1 if x=7; is 2 if x=463; is 3 if x=4819.

Mathematica

f[ x_] := EulerPhi[ DivisorSigma[1, x]] - DivisorSigma[1, EulerPhi[x]]; t = {}; Do[ s = f[n]; If[ s != 0 && Mod[ s, n + 1] == 0, Print[n]; AppendTo[t, n], {n, 2*10^8}]; t

Crossrefs

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

Sequence in context: A220306 A344106 A346987 * A048363 A254473 A183613

Adjacent sequences: A092583 A092584 A092585 * A092587 A092588 A092589

Keyword

nonn

Author

Labos Elemer, Mar 01 2004

Extensions

Edited and extended by Robert G. Wilson v, Mar 03 2004

a(33)-a(34) from Donovan Johnson, Mar 04 2013

Status

approved