A053339 Squarefree terms of A050530 with 3 prime divisors.
255, 435, 455, 561, 595, 665, 705, 795, 805, 885, 957, 1001, 1105, 1295, 1309, 1335, 1463, 1495, 1551, 1605, 1615, 1645, 1729, 1749, 1855, 1885, 1947, 1955, 2001, 2055, 2065, 2091, 2093, 2185, 2235, 2345, 2387, 2405, 2465, 2555, 2703, 2717, 2755, 2821
Offset: 1
Keywords
Examples
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]
Links
- G. C. Greubel, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Select[Range[3000],PrimeQ[#-EulerPhi[#]]&],SquareFreeQ[3] && PrimeOmega[#]==3&] (* Harvey P. Dale, Jun 23 2013 *)
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PARI
isok(n) = isprime(n-eulerphi(n)) && issquarefree(n) && (omega(n)==3); \\ Michel Marcus, May 31 2018
Formula
Numbers k = pqr such that A051953(k) = k - EulerPhi(k) is a prime of polynomial form pq + pr + qr - p - q - r + 1.