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A173286 2*prime(prime(prime(n)))-3 and 3*prime(prime(prime(n)))-2 are both primes. 1
1, 2, 5, 8, 9, 15, 26, 53, 63, 86, 92, 93, 95, 116, 137, 152, 233, 254, 281, 303, 329, 334, 352, 386, 392, 415, 423, 460, 470, 476, 508, 565, 570, 601, 660, 673, 680, 725, 748, 898, 907, 942, 948, 952, 958, 1045, 1119, 1126, 1138, 1140, 1259, 1314, 1360 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..53.

EXAMPLE

a(1) = 1 because 2*p(p(p(1)))-3 = 7 = prime and 3*p(p(p(1)))-2 = 13 = prime;

a(2) = 2 because 2*p(p(p(2)))-3 = 19 = prime and 3*p(p(p(2)))-2 = 31 = prime;

a(3) = 5 because 2*p(p(p(5)))-3 = 379 = prime and 3*p(p(p(5)))-2 = 251 = prime;

a(4) = 8 because 2*p(p(p(8)))-3 = 991 = prime and 3*p(p(p(8)))-2 = 659 = prime;

a(5) = 9 because 2*p(p(p(9)))-3 = 1291 = prime and 3*p(p(p(9)))-2 = 859 = prime;

a(6) = 15 because 2*p(p(p(15)))-3 = 3889 = prime and 3*p(p(p(15)))-2 = 2591 = prime.

MATHEMATICA

pppQ[n_]:=Module[{p=Prime[Prime[Prime[n]]]}, AllTrue[{2p-3, 3p-2}, PrimeQ]]; Select[Range[1400], pppQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 25 2016 *)

PROG

(PARI) isok(n) = isprime(2*prime(prime(prime(n)))-3) && isprime(3*prime(prime(prime(n)))-2); \\ Michel Marcus, Sep 02 2013

CROSSREFS

Cf. A038580, A063908, A088878.

Sequence in context: A026448 A258353 A050678 * A243182 A088620 A068702

Adjacent sequences:  A173283 A173284 A173285 * A173287 A173288 A173289

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Feb 15 2010

EXTENSIONS

Extended beyond 15 by R. J. Mathar, Mar 01 2010

STATUS

approved

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Last modified September 29 17:14 EDT 2020. Contains 337432 sequences. (Running on oeis4.)