A256907 Numbers n such that phi(n) = 3*phi(n+1).

119, 527, 545, 2849, 3689, 4487, 6649, 18619, 26771, 30377, 44659, 47585, 50507, 76997, 83021, 102167, 112463, 128933, 138773, 163877, 174437, 192881, 193115, 198263, 217967, 236441, 243827, 244001, 254539, 268067, 282359, 287825, 298115, 345059, 410123, 464645

Offset: 1

Author

Mauro Fiorentini, Apr 12 2015

Keywords

• nonn

Examples

			phi(545) = 3*phi(546) = 432.
		

Links

• Mauro Fiorentini, Table of n, a(n) for n = 1..755 (all terms with n <= 10^9).

Crossrefs

Cf. A171262.

Programs

Magma

[n: n in [1..2*10^6] | EulerPhi(n) eq 3*EulerPhi(n+1)]; // Vincenzo Librandi, Apr 13 2015

Mathematica

Select[Range@ 1000000, EulerPhi@# == 3 EulerPhi[# + 1] &] (* Michael De Vlieger, Apr 12 2015 *)

PARI

s=[]; for(n=1, 1000000, if(eulerphi(n)==3*eulerphi(n+1), s=concat(s, n))); s \\ Colin Barker, Apr 12 2015