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A115919 Numbers n such that sigma(n)-phi(n) is a prime number. 5
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 (list; graph; refs; listen; history; text; internal format)
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: A195943 A096165 A164336 * A038701 A127072 A056781

Adjacent sequences:  A115916 A115917 A115918 * A115920 A115921 A115922

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 06 2006

STATUS

approved

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Last modified January 27 09:01 EST 2020. Contains 331293 sequences. (Running on oeis4.)