OFFSET
1,2
LINKS
Harry J. Smith, Table of n, a(n) for n=1..1000
EXAMPLE
sigma(10) + 1 = 18 + 1 = 19 (prime). sigma(24) + 1 = 60 + 1 = 61 (prime).
MAPLE
select(isprime @ (1+numtheory:-sigma), [$1..1000]); # Robert Israel, May 29 2015
MATHEMATICA
Select[ Range[170], PrimeQ[ DivisorSigma[1, # ] + 1] & ]
PROG
(PARI) { n=0; for (m=1, 10^9, if (isprime(sigma(m) + 1), write("b065512.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 20 2009
(Magma) [n: n in [1..200] | IsPrime(1+SumOfDivisors(n))]; // Vincenzo Librandi, May 30 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Nov 26 2001
STATUS
approved