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Numbers k such that k + D(k) + 1 is prime, where D() are the doublets, A020338.
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%I #18 Feb 25 2022 10:42:41

%S 1,3,5,6,8,9,10,11,13,14,15,21,23,25,28,30,31,34,35,36,38,45,49,50,53,

%T 60,63,64,66,69,71,74,76,79,80,81,83,90,91,99,101,105,106,108,110,113,

%U 114,124,128,130,134,135,136,140,141,143,144,150,151,159,161,163,165

%N Numbers k such that k + D(k) + 1 is prime, where D() are the doublets, A020338.

%H Robert Israel, <a href="/A121882/b121882.txt">Table of n, a(n) for n = 1..10000</a>

%e 9 is a term because 9 + 99 + 1 = 109 is prime.

%p filter:= n -> isprime(1+n*(2+10^(1+ilog10(n)))):

%p select(filter, [$1..1000]);# _Robert Israel_, Feb 23 2022

%o (PARI) isok(k) = isprime(k + eval(Str(k, k)) + 1); \\ _Michel Marcus_, Feb 25 2022

%Y Cf. A020338.

%K base,easy,nonn

%O 1,2

%A _Jason Earls_, Aug 31 2006