A092585 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.

2, 4, 16, 64, 151, 449, 3403, 4096, 4267, 9307, 35905, 65536, 247285, 262144, 17625601, 33126625, 399288961, 649232833, 947278081, 1073741824, 2102485441, 4555788385, 5203567081, 6103058177, 7115716609

Offset

1,1

Links

Table of n, a(n) for n=1..25.

Example

(sigma(phi(x))-phi(sigma(x)))/(x-1) is -1 if x=2,4,16,64,4096,65536,262144 and is 2 if x=151,449,3403, etc.

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, A065395.

Sequence in context: A001901 A127588 A187822 * A106186 A155543 A151371

Adjacent sequences: A092582 A092583 A092584 * A092586 A092587 A092588

Keyword

nonn

Author

Labos Elemer, Mar 01 2004

Extensions

More terms from Robert G. Wilson v, Mar 03 2004

a(17)-a(25) from Donovan Johnson, Mar 04 2013

Status

approved