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A066653 Squarefree numbers k such that the pair 2*k +- 1 is a twin prime pair. 4
2, 3, 6, 15, 21, 30, 51, 69, 114, 141, 174, 210, 231, 285, 309, 321, 330, 411, 429, 510, 546, 615, 645, 651, 714, 741, 834, 849, 861, 894, 939, 966, 1041, 1065, 1119, 1155, 1191, 1329, 1365, 1401, 1626, 1686, 1695, 1731, 1770 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = 3*A355846(n-1), for n >= 2. - Wesley Ivan Hurt, Jul 24 2022
EXAMPLE
2*a(6) +/- 1 = 2*30 +/- 1 = (59, 61) = (A000040(17), A000040(18)) = (A001359(7), A006512(7)) = (A066652(10), A066651(13)).
MATHEMATICA
Select[Range[2000], SquareFreeQ[#] && And @@ PrimeQ[2# + {-1, 1}] &] (* Amiram Eldar, Dec 19 2019 *)
PROG
(Magma) [k:k in [1..2000]|IsSquarefree(k) and IsPrime(2*k-1) and IsPrime(2*k+1)]; // Marius A. Burtea, Dec 19 2019
(PARI) isok(k) = issquarefree(k) && isprime(2*k-1) && isprime(2*k+1); \\ Michel Marcus, Jul 25 2022
CROSSREFS
Sequence in context: A090983 A198684 A293534 * A081945 A329745 A255353
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 10 2002
STATUS
approved

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Last modified July 15 11:16 EDT 2024. Contains 374332 sequences. (Running on oeis4.)