A115919 Numbers k such that sigma(k) - phi(k) is a prime number.

2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, 23, 25, 29, 31, 32, 36, 37, 41, 43, 47, 50, 53, 59, 61, 67, 71, 73, 79, 81, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 225, 227

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

Cf. A038344.

Sequence in context: A096165 A164336 A348263 * A038701 A127072 A341089

Adjacent sequences: A115916 A115917 A115918 * A115920 A115921 A115922

Keyword

nonn

Author

Giovanni Resta, Feb 06 2006

Status

approved