This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A051647 #24 Feb 24 2025 02:03:10 %S A051647 2,3,5,7,11,13,17,23,29,47,53,59,67,73,83,89,101,137,139,157,163,179, %T A051647 181,191,193,223,229,251,271,277,281,313,317,347,349,353,359,401,419, %U A051647 421,431,433,449,457,463,479,523,577,599,601,631,653,701,709,719,727 %N A051647 Primes p such that 210*p + 1 is also prime. %C A051647 Analogous to A005384, Sophie Germain primes. %C A051647 A002110(4)*p + 1 = 210*p + 1 and p are both primes. %H A051647 Amiram Eldar, <a href="/A051647/b051647.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Vincenzo Librandi) %F A051647 a(n) = (A051648(n)-1)/210. - _Amiram Eldar_, Feb 24 2025 %e A051647 11 is in the sequence because 210*11 + 1 = 2311 is also prime. %t A051647 Select[Prime[Range[200]],PrimeQ[210#+1]&] (* _Harvey P. Dale_, Apr 25 2011 *) %o A051647 (Magma) [p: p in PrimesUpTo(900) | IsPrime(210*p+1)]; // _Vincenzo Librandi_, Apr 11 2013 %o A051647 (PARI) isok(k) = isprime(k) && isprime(210*k+1); \\ _Amiram Eldar_, Feb 24 2025 %Y A051647 Cf. A005384, A005385, A007693, A051648. %K A051647 nonn,easy %O A051647 1,1 %A A051647 _Labos Elemer_