OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
sigma(81) - phi(81) = 67, a prime.
MATHEMATICA
Select[Range[300], PrimeQ[DivisorSigma[1, #]-EulerPhi[#]]&] (* Harvey P. Dale, Feb 25 2011 *)
PROG
(PARI) is(n)=isprime(sigma(n)-eulerphi(n)) \\ Charles R Greathouse IV, Nov 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 06 2006
STATUS
approved