login
This site is supported by donations to The OEIS Foundation.

 

Logo

The OEIS is looking to hire part-time people to help edit core sequences, upload scanned documents, process citations, fix broken links, etc. - Neil Sloane, njasloane@gmail.com

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A108403 Numbers n such that n^2-6 and n^2+6 are both prime. 1
5, 25, 65, 145, 355, 605, 985, 1075, 1295, 1465, 1565, 1675, 1915, 2345, 2425, 2585, 2755, 3005, 3155, 3785, 4595, 4625, 4975, 5225, 5465, 5665, 5905, 5915, 6115, 6295, 6305, 6415, 6485, 7235, 7775, 8185, 9065, 9275, 9415, 9755, 9835, 10145, 10195 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All members of the sequence are divisible by 5 as if n is 1 or 4 mod 5 then n^2-6 is divisible by 5 and if n is 2 or 3 mod 5 then n^2+6 is divisible by 5.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

a(2)=25 since 25^2 - 6 = 619 and 25^2 + 6 = 631 are both prime.

MATHEMATICA

pQ[n_]:=Module[{n2=n^2}, And@@PrimeQ[{n2-6, n2+6}]]; Select[5Range[2100], pQ]  (* Harvey P. Dale, Nov 06 2011 *)

PROG

(MAGMA) [n: n in [2..100000] | IsPrime(n^2-6) and IsPrime(n^2+6)] // Vincenzo Librandi, Nov 13 2010

CROSSREFS

Cf. A087681 (with n instead of n^2), A108701 (with 2 instead of 6).

Sequence in context: A146404 A179131 A054994 * A007058 A071383 A088959

Adjacent sequences:  A108400 A108401 A108402 * A108404 A108405 A108406

KEYWORD

nonn

AUTHOR

John L. Drost, Jul 04 2005

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified May 26 09:12 EDT 2017. Contains 287093 sequences.