A064805 Numbers k such that phi(k) > phi(k+2).

13, 16, 19, 22, 23, 25, 28, 31, 34, 37, 38, 40, 43, 46, 47, 49, 52, 53, 55, 58, 61, 64, 67, 68, 73, 76, 79, 82, 83, 85, 86, 88, 89, 91, 94, 97, 98, 100, 103, 106, 109, 112, 113, 115, 118, 121, 124, 127, 128, 130, 131, 133, 134, 136, 139, 142, 143, 145, 148, 151, 152

Offset: 1

Author

Robert G. Wilson v, Oct 21 2001

Keywords

• easy
• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010 (phi), A001837.

Programs

Mathematica

Select[ Range[150], EulerPhi[ # ] > EulerPhi[ #+2 ] & ]
Position[Partition[EulerPhi[Range[200]],3,1],?(First[#]>Last[#]&), 1, Heads->False]//Flatten (* _Harvey P. Dale, Jun 14 2017 *)

PARI

{ n=0; for (m=1, 10^9, f=eulerphi(m); if (eulerphi(m)>eulerphi(m + 2), write("b064805.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Sep 26 2009

Extensions

a(60)-a(61) from Harry J. Smith, Sep 26 2009