OFFSET
1,1
COMMENTS
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10622
EXAMPLE
289 is in the sequence because 2*289 - 1 = 577 and sigma(289) = 307 (both primes).
MATHEMATICA
Select[Range[10^7], PrimeQ[2 # - 1] && PrimeQ[DivisorSigma[1, #]] &] (* Vincenzo Librandi, Nov 15 2014 *)
PROG
(Magma) [n: n in [2..10000000] | IsPrime(2*n-1) and IsPrime(SumOfDivisors(n))];
(PARI) for(n=1, 10^6, if(isprime(2*n-1)&&isprime(sigma(n)), print1(n, ", "))) \\ Derek Orr, Nov 14 2014
(Python)
from sympy import isprime, divisor_sigma
A249902_list = [2]+[n for n in (d**2 for d in range(1, 10**3)) if isprime(2*n-1) and isprime(divisor_sigma(n))] # Chai Wah Wu, Jul 23 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Nov 14 2014
STATUS
approved