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A239732 Primes p such that 2p+9 and 9p+2 are both prime. 1
5, 11, 19, 29, 31, 71, 101, 109, 131, 151, 179, 211, 229, 239, 269, 281, 311, 491, 521, 541, 719, 739, 751, 809, 919, 929, 971, 1051, 1061, 1129, 1181, 1291, 1361, 1439, 1481, 1621, 1741, 1811, 1831, 2111, 2131, 2221, 2371, 2389, 2411, 2521, 2539, 2549, 2689, 2791 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
All of the numbers in this sequence, except a(1), are either 1 or 9 mod 10.
LINKS
EXAMPLE
5 is prime, 2*5+9 = 19 is prime, and 9*5+2 = 47 is prime. Thus, 5 is a member of this sequence.
MATHEMATICA
Select[Prime[Range[500]], And@@PrimeQ[{2#+9, 9#+2}]&] (* Harvey P. Dale, Apr 23 2014 *)
PROG
(Python)
import sympy
from sympy import isprime
{print(n) for n in range(5000) if isprime(2*n+9) and isprime(9*n+2) and isprime(n)}
(PARI) s=[]; forprime(p=2, 3000, if(isprime(2*p+9) && isprime(9*p+2), s=concat(s, p))); s \\ Colin Barker, Mar 26 2014
CROSSREFS
Sequence in context: A275068 A038872 A141158 * A130828 A244241 A108151
KEYWORD
nonn,easy
AUTHOR
Derek Orr, Mar 25 2014
STATUS
approved

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Last modified March 29 01:36 EDT 2024. Contains 371264 sequences. (Running on oeis4.)