OFFSET
1,1
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3) = 5: sigma(sigma(5))-sigma(5)+1 = 12-6+1 = 7, which is prime.
a(10) = 15: sigma(sigma(15))-sigma(15)+1 = 60-24+1 = 37, which is prime.
MAPLE
with(numtheory):KD := proc() local a; a:= sigma(sigma(n))-sigma(n)+1; if isprime(a) then RETURN (n); fi; end: seq(KD(), n=1..500);
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Nov 11 2013
STATUS
approved