OFFSET
1,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..10000
FORMULA
Numbers k = pqr such that A051953(k) = k - EulerPhi(k) is a prime of polynomial form pq + pr + qr - p - q - r + 1.
EXAMPLE
435 = 3*5*29 and 435 - Phi(435) = 3*5 + 3*29 + 5*29 - 3 - 5 - 29 + 1 = 211, the 47th prime. [corrected by Jon E. Schoenfield, May 30 2018]
MATHEMATICA
Select[Select[Range[3000], PrimeQ[#-EulerPhi[#]]&], SquareFreeQ[3] && PrimeOmega[#]==3&] (* Harvey P. Dale, Jun 23 2013 *)
PROG
(PARI) isok(n) = isprime(n-eulerphi(n)) && issquarefree(n) && (omega(n)==3); \\ Michel Marcus, May 31 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jan 05 2000
STATUS
approved