A123998: No primes except 3?

[zak seidov]

Why are there no prime numbers except of 3,
in this sequence?
Zak

A123998
={1,3,9,15,18,39,48,69,78,99,105,114,135,153,165,168,183,189,219,249,273,

288,300,303,309,330,345,363,405,414,438,468,483,498,504,534,585,618,
 639,648,699,714,729,765,804,813,828,879,933}; 
(* %N A123998 Numbers n for which 2n+1 and 4n+1 are
primes. *)



 
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