A092585 Numbers k such that sigma(phi(k))-phi(sigma(k)) is nonzero and is divisible by (k-1), that is A065395(k)/(k-1) = (phi(sigma(k))-sigma(phi(k)))/(k-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

Author

Labos Elemer, Mar 01 2004

Keywords

• nonn
• more

Examples

			(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.
		

Crossrefs

Cf. A033632, A092584-A092588, A065395.

Programs

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

Extensions

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

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