A053339 - OEIS

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

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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