OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
A106483(n) = prime(a(n)) . - R. J. Mathar, Aug 20 2019
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
KEYWORD
easy,nonn
AUTHOR
mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Feb 19 2004
STATUS
approved