login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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
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}]
Select[Range[600], AllTrue[{#^2+#-1, 2#^2+2#-1}, PrimeQ]&] (* Harvey P. Dale, Dec 02 2021 *)
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
Subsequence of A045546.
Sequence in context: A309830 A008770 A347548 * A030068 A239958 A008769
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Oct 21 2013
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 02:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)