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Numbers k such that 4+k and 4*k+1 are prime.
4

%I #15 Sep 27 2024 05:41:26

%S 1,3,7,9,13,15,25,27,37,39,43,49,57,67,69,79,93,97,99,105,127,135,153,

%T 163,169,175,177,189,193,207,219,235,253,265,267,273,277,279,303,307,

%U 309,343,345,363,405,417,427,435,475,483,487,499,517,553,559,567,573

%N Numbers k such that 4+k and 4*k+1 are prime.

%C Except for 3, no terms == 3 or 5 (mod 7). - _Robert Israel_, Jul 26 2019

%H Robert Israel, <a href="/A120226/b120226.txt">Table of n, a(n) for n = 1..10000</a>

%p select(t -> isprime(t+4) and isprime(4*t+1), [seq(i,i=1..1000,2)]); # _Robert Israel_, Jul 26 2019

%t Select[Range[600],AllTrue[{4+#,4#+1},PrimeQ]&] (* _Harvey P. Dale_, Nov 14 2022 *)

%Y Cf. A092945, A106057, A085063, A120223, A120224, A120225, A120227.

%K nonn

%O 1,2

%A _Zak Seidov_, Jun 10 2006