OFFSET
1,1
COMMENTS
EXAMPLE
17 is in the sequence because phi(17) = 16 = 2*phi(15) = 2*8.
MATHEMATICA
Select[Prime@ Range@ 500, Function[p, AnyTrue[Range[p - 2], p - 1 == # EulerPhi[p - #] &]]] (* Michael De Vlieger, Jan 09 2016, Version 10 *)
PROG
(Magma) Set(Sort([[n: k in [1..n-2] | IsPrime(n) and EulerPhi(n) eq k*EulerPhi(n-k)]: n in [1..10000]]))
(Magma) Set(Sort([5] cat [n: n in [6..100000], k in [1..5] | IsPrime(n) and EulerPhi(n) eq k*EulerPhi(n-k)]))
(PARI) listp(nn) = {forprime(p=2, nn, for (k=1, p-2, if (eulerphi(p) == k*eulerphi(p-k), print1(p, ", "); break)); ); } \\ Michel Marcus, Dec 27 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Dec 26 2015
STATUS
approved