OFFSET
1,1
COMMENTS
EXAMPLE
10 is in the sequence because sigma(10-1) = sigma(9) = 13 and sigma(phi(10)) = sigma(4) = 7 (both primes).
MATHEMATICA
Select[Range[10^6], And[PrimeQ@ DivisorSigma[1, # - 1], PrimeQ@ DivisorSigma[1, EulerPhi@ #]] &] (* Michael De Vlieger, Mar 17 2016 *)
PROG
(Magma) [n: n in [2..100000] | IsPrime(SumOfDivisors(n-1)) and IsPrime(SumOfDivisors(EulerPhi(n)))]
(PARI) isok(n) = isprime(sigma(n-1)) && isprime(sigma(eulerphi(n))); \\ Michel Marcus, Mar 17 2016
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Mar 16 2016
STATUS
approved