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A053339 Squarefree terms of A050530 with 3 prime divisors. 1
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 (list; graph; refs; listen; history; text; internal format)
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

Cf. A051953, A050530.

Sequence in context: A023690 A101745 A182221 * A031197 A043348 A031469

Adjacent sequences:  A053336 A053337 A053338 * A053340 A053341 A053342

KEYWORD

nonn

AUTHOR

Labos Elemer, Jan 05 2000

STATUS

approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)