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A230515 Numbers n such that n*(n+1)-1 is a Sophie Germain prime. 2
2, 3, 5, 6, 9, 11, 15, 20, 38, 39, 45, 48, 50, 54, 59, 93, 126, 131, 144, 149, 153, 174, 176, 218, 231, 236, 240, 246, 248, 263, 285, 306, 309, 330, 335, 374, 380, 395, 396, 401, 419, 423, 449, 455, 468, 471, 474, 495, 501, 506, 549, 551, 560, 588 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence is interesting because of the conjecture associated with A230514.

LINKS

Zhi-Wei Sun, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 2 since 2*3 - 1 = 5 is a Sophie Germain prime.

a(2) = 3 since 3*4 - 1 = 11 is a Sophie Germain prime.

a(3) = 5 since 5*6 - 1 = 29 is a Sophie Germain prime but 4*5 - 1 = 19 is not.

MATHEMATICA

q[n_]:=PrimeQ[n(n+1)-1]&&PrimeQ[2n(n+1)-1]

m=0

Do[If[q[n], m=m+1; Print[m, " ", n]], {n, 1, 506}]

PROG

(MAGMA) [n: n in [1..600] | IsPrime(n*(n+1)-1) and IsPrime(2*n*(n+1)-1)]; // Bruno Berselli, Oct 22 2013

CROSSREFS

Cf. A000040, A005384, A230514.

Subsequence of A045546.

Sequence in context: A008772 A008771 A008770 * A030068 A239958 A008769

Adjacent sequences:  A230512 A230513 A230514 * A230516 A230517 A230518

KEYWORD

nonn

AUTHOR

Zhi-Wei Sun, Oct 21 2013

STATUS

approved

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Last modified March 21 04:59 EDT 2019. Contains 321364 sequences. (Running on oeis4.)