A079445 phi(n)*(n-phi(n))-1 is prime.

4, 5, 6, 7, 9, 10, 12, 13, 14, 18, 19, 21, 24, 26, 28, 31, 35, 38, 39, 40, 42, 43, 44, 45, 49, 50, 51, 54, 55, 58, 61, 63, 66, 68, 70, 72, 73, 74, 75, 76, 77, 84, 86, 90, 91, 92, 93, 94, 98, 99, 100, 102, 103, 104, 108, 109, 116, 119, 122, 129, 133, 139, 141

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

a(1)=4 as phi(4)=2, 2*[4-2]-1=3.

Mathematica

pepQ[n_]:=Module[{ep=EulerPhi[n]}, PrimeQ[ep(n-ep)-1]]; Select[ Range[ 150], pepQ] (* Harvey P. Dale, Jun 11 2018 *)

Prog

(PARI) for (n=2, 100, if (isprime(eulerphi(n)*(n-eulerphi(n))-1), print1(n", ")))

Crossrefs

Cf. A079446.

Sequence in context: A329782 A218044 A066485 * A120173 A075862 A088685

Adjacent sequences: A079442 A079443 A079444 * A079446 A079447 A079448

Keyword

nonn

Author

Jon Perry, Jan 09 2003

Extensions

More terms from Michel Marcus, Mar 17 2014

Status

approved