OFFSET
1,1
COMMENTS
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
MAPLE
F:= proc(n)
local r;
r:= numtheory:-sigma(n)-1;
if isprime(r) then r else NULL fi
end proc:
seq(F(n), n=1..1000); # Robert Israel, Nov 02 2014
MATHEMATICA
a248793[n_Integer] :=
Cases[DivisorSigma[1, #] - 1 & /@ Range[n], _?PrimeQ]; a248793[104] (* Michael De Vlieger, Nov 07 2014 *)
PROG
(Magma) [a: n in [1..1000] | IsPrime(a) where a is SumOfDivisors(n)-1]
(PARI) for(n=1, 10^3, if(isprime(sigma(n)-1), print1(sigma(n)-1, ", "))) \\ Derek Orr, Nov 01 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jaroslav Krizek, Nov 01 2014
STATUS
approved