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 A087031 #12 Jul 02 2018 12:41:25 %S A087031 1,3,9,15,27,31,33,39,47,57,61,63,69,75,91,93,99,105,115,117,123,135, %T A087031 141,147,151,159,167,177,183,185,189,195,199,213,217,219,225,237,245, %U A087031 251,257,267,271,273,279,297,301,303,309,325,341,345,361,367,375 %N A087031 Numbers n such that 2p-n is prime, p is the smallest prime > n. %H A087031 Charles R Greathouse IV, <a href="/A087031/b087031.txt">Table of n, a(n) for n = 1..10000</a> %e A087031 3 is a term because smallest prime >3 is 5 and 2*5-3=7 is prime. %t A087031 Select[Range[400],PrimeQ[2*NextPrime[#]-#]&] (* _Harvey P. Dale_, Jul 02 2018 *) %o A087031 (PARI) isok(n) = isprime(2*nextprime(n+1) - n); \\ _Michel Marcus_, Oct 03 2013 %Y A087031 Cf. A087030. %K A087031 easy,nonn %O A087031 1,2 %A A087031 _Zak Seidov_, Jul 31 2003 %E A087031 Corrected by _Michel Marcus_, Oct 03 2013