OFFSET
1,1
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..2450
EXAMPLE
a(6)= 167: sigma(32)+sigma(sigma(32))= 63+104= 167, which is prime.
a(11)= 383: sigma(93)+sigma(sigma(93))= 128+255= 383, which is prime.
MAPLE
with(numtheory):KD := proc() local a; a:= sigma(n)+sigma(sigma(n)); if isprime(a) then RETURN (a); fi; end:seq(KD(), n=1..5000);
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Nov 10 2013
STATUS
approved