OFFSET
1,3
COMMENTS
Numbers n such that 2*n^2 + 3 and 2*n^2 + 5 are both prime.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
2 is in this sequence because 2*2^2 + 3 = 11 and 2*2^2 + 5 = 13 are both prime.
MATHEMATICA
a247175[n_Integer] := Select[Range[n], And[PrimeQ[2*(#^2 + 2) - 1], PrimeQ[2*(#^2 + 2) + 1]] &]; a247175[4500] (* Michael De Vlieger, Nov 30 2014 *)
Select[Range[0, 4500], AllTrue[2#^2+{3, 5}, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Feb 09 2019 *)
PROG
(Magma) [ n: n in [0..4500] | IsPrime(2*(n^2+2)-1) and IsPrime(2*(n^2+2)+1) ];
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Nov 30 2014
STATUS
approved