OFFSET
1,1
COMMENTS
EXAMPLE
17 is in the sequence because sigma(17-1) = sigma(16) = 31 and sigma(10) - 1 = 18 - 1 = 17 (both primes).
MATHEMATICA
Select[Range[10^7], And[PrimeQ@ DivisorSigma[1, # - 1], PrimeQ[DivisorSigma[1, #] - 1]] &] (* Michael De Vlieger, Mar 17 2016 *)
PROG
(Magma) [n: n in [2..10000000] | IsPrime(SumOfDivisors(n-1)) and IsPrime(SumOfDivisors(n)-1)]
(PARI) isok(n) = isprime(sigma(n-1)) && isprime(sigma(n)-1); \\ Michel Marcus, Mar 17 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Mar 16 2016
STATUS
approved