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A092058 Numbers n such that 2*prime(n)^2 - 1 is prime. 5
1, 2, 4, 5, 6, 7, 13, 14, 17, 21, 29, 30, 31, 33, 37, 41, 42, 45, 46, 47, 54, 56, 59, 62, 64, 71, 73, 75, 80, 81, 84, 93, 103, 105, 106, 113, 114, 120, 126, 131, 132, 134, 139, 141, 144, 145, 146, 148, 159, 160, 169, 175, 179, 183, 185, 186, 188, 192, 212, 217, 220 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

EXAMPLE

2*prime(1)^2 - 1 = 7 is prime so a(1)=1;

2*prime(2)^2 - 1 = 17 is prime so a(2)=2;

2*prime(3)^2 - 1 = 97 is not prime;

2*prime(4)^2 - 1 = 241 is prime so a(3)=4.

MATHEMATICA

Select[Range[500], PrimeQ[2Prime[#]^2-1]&] (* Harvey P. Dale, Dec 13 2010 *)

PROG

(PARI) for (i=1, 300, if(isprime(2*prime(i)^2-1), print1(i, ", ")))

(MAGMA) [n: n in [1..220]| IsPrime(2*NthPrime(n)^2-1)]; // Vincenzo Librandi, Jan 18 2013

CROSSREFS

Cf. A092057.

Sequence in context: A039057 A317185 A276005 * A134532 A282278 A268448

Adjacent sequences:  A092055 A092056 A092057 * A092059 A092060 A092061

KEYWORD

easy,nonn

AUTHOR

mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Feb 19 2004

STATUS

approved

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Last modified March 21 22:19 EDT 2019. Contains 321382 sequences. (Running on oeis4.)