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A265851
Primes p such that phi(p-2) = phi(p+5) - 2.
1
5, 11, 17, 257, 65537
OFFSET
1,1
COMMENTS
Also primes p such that cototient(p-2) = cototient(p+5) - 5, where cototient(x) = A051953(x).
The next term, if it exists, must be greater than 5*10^8.
The first 4 known Fermat primes > 3 from A019434 are in the sequence.
Primes from A265850.
EXAMPLE
Prime 17 is in the sequence because phi(15) = phi(22) - 2 = 8.
MATHEMATICA
Select[Prime@ Range[10^4], EulerPhi[# - 2] == EulerPhi[# + 5] - 2 &] (* Michael De Vlieger, Dec 17 2015 *)
PROG
(Magma) [n: n in [3..10^7] | IsPrime(n) and EulerPhi(n-2) eq EulerPhi(n+5) - 2]
(PARI) is(n)=eulerphi(n-2)==eulerphi(n+5)-2 \\ Anders Hellström, Dec 16 2015
(Magma) [p: p in PrimesInInterval(3, 2*10^5) | EulerPhi(p-2) eq EulerPhi(p+5)-2]; // Vincenzo Librandi, Dec 17 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Dec 16 2015
STATUS
approved