A192221 Numbers n such that phi(n-2)=phi(n+2) where phi=A000010.

10, 16, 18, 22, 37, 54, 66, 93, 142, 150, 246, 294, 405, 457, 618, 630, 774, 803, 1013, 1026, 1110, 1146, 1254, 1272, 1297, 1458, 1590, 1686, 1822, 1830, 2032, 2166, 2454, 2625, 2646, 2662, 2694, 2934, 3030, 3218, 3323, 3510, 3990, 4266, 4342, 4374, 4614, 4806, 4854, 4950, 5182, 5286

Offset: 1

Author

Juri-Stepan Gerasimov, Jun 26 2011

Keywords

• nonn

Crossrefs

Cf. A000010, A066812.

Programs

Mathematica

Select[Range[3, 5000], EulerPhi[# - 2] == EulerPhi[# + 2] &] (* Alonso del Arte, Jun 28 2011 *)
Flatten[Position[Partition[EulerPhi[Range[5300]],5,1],?(#[[1]] == #[[5]]&), 1,Heads -> False]]+2 (* _Harvey P. Dale, Jul 01 2019 *)

PARI

for(n=3,1e4,if(eulerphi(n-2)==eulerphi(n+2),print1(n", "))) \\ Charles R Greathouse IV, Jun 27 2011

Formula

a(n) = A179186(n)+2. - R. J. Mathar, Jun 26 2011