A075749 - OEIS

%I #26 Sep 08 2022 08:45:07

%S 2,5,11,13,16,28,29,30,35,36,42,44,50,51,55,57,73,86,104,121,125,128,

%T 135,140,147,148,157,158,160,161,165,168,179,193,204,205,209,223,244,

%U 247,249,251,255,264,271,273,277,281,282,290,302,304,310,312,313,316

%N Numbers k such that 210*k +- 1 are twin primes.

%H Amiram Eldar, <a href="/A075749/b075749.txt">Table of n, a(n) for n = 1..10000</a>

%e k = 2 is a term since 210*2 - 1 = 419 and 210*2 + 1 = 421 are twin primes.

%t Select[Range[6! ],PrimeQ[210*#-1]&&PrimeQ[210*#+1]&] (* _Vladimir Joseph Stephan Orlovsky_, Apr 08 2010 *)

%o (PARI) isok(n) = isprime(210*n+1) && isprime(210*n-1); \\ _Michel Marcus_, Jan 14 2015

%o (Magma) [k:k in [1..320]| IsPrime(210*k-1) and IsPrime(210*k+1)]; // _Marius A. Burtea_, Jan 01 2020

%Y Cf. A002822 (with 6*k +- 1), A176114 (with 30*k +- 1).

%K easy,nonn

%O 1,1

%A _Zak Seidov_, Oct 08 2002