OFFSET
1,1
EXAMPLE
7 is prime, 2*7 + 1 = 15 is composite, so a(1) = 7*2 = 14.
MAPLE
a:=proc(n) if isprime(2*ithprime(n)+1)=false then 2*ithprime(n) else fi end: seq(a(n), n=1..100); # Emeric Deutsch, Jul 25 2006
MATHEMATICA
2Select[Range[375], PrimeQ[#]&&!PrimeQ[2#+1]&] (* Stefano Spezia, Aug 02 2024 *)
PROG
(PARI) forprime (p=3, 200, if (isprime(2*p+1), print1(2*p", ")))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jon Perry, Jan 31 2003
EXTENSIONS
More terms from Emeric Deutsch, Jul 25 2006
STATUS
approved