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A023228
Numbers k such that k and 8*k + 1 are both prime.
9
2, 5, 11, 17, 29, 71, 101, 107, 131, 137, 149, 179, 239, 269, 347, 401, 431, 449, 479, 491, 509, 557, 599, 617, 659, 677, 761, 809, 821, 857, 929, 941, 947, 977, 1151, 1187, 1229, 1289, 1307, 1361, 1367, 1409, 1487, 1559, 1571, 1601, 1619, 1667, 1697, 1811, 1871
OFFSET
1,1
LINKS
Samuel S. Wagstaff, Jr., Sum of Reciprocals of Germain Primes, Journal of Integer Sequences, Vol. 24, No. 2 (2021), Article 21.9.5.
FORMULA
Sum_{n>=1} 1/a(n) is in the interval (1.151956749, 1.4207187) (Wagstaff, 2021). - Amiram Eldar, Nov 04 2021
MATHEMATICA
Select[Prime[Range[2000]], PrimeQ[8# + 1]&] (* Vincenzo Librandi, Feb 02 2014 *)
PROG
(Magma) [ p: p in PrimesUpTo(1900) | IsPrime(8*p+1) ]; // Klaus Brockhaus, Dec 21 2008
(PARI) list(lim)=my(v=List()); forprime(p=2, lim, if(isprime(8*p+1), listput(v, p))); Vec(v) \\ Charles R Greathouse IV, Oct 20 2021
CROSSREFS
Cf. A007519 (primes of form 8n+1), A005123 ((( primes == 1 mod 8 ) - 1)/8). - Klaus Brockhaus, Dec 21 2008
Sequence in context: A228353 A055499 A014424 * A027429 A336376 A059987
KEYWORD
nonn,easy
STATUS
approved