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 A256823 #23 Sep 15 2019 04:06:43 %S A256823 4,7,9,11,27,40,63,80,120,173,227,358,445,525,767,1164,2180,5368,7898 %N A256823 Numbers n such that A257378(n)=A257379(n), so the prime numbers k*n*2^n-1 and k*n*2^n+1 are twin primes for the smallest k such that k*n*2^n-1 is a prime number. %C A256823 The k values are in A257378 and A257379. %o A256823 (PARI) a8(n) = my(k=1); while(!isprime(k*n*2^n+1), k+=2); k; %o A256823 a9(n) = my(k=1); while(!isprime(k*n*2^n-1), k+=2); k; %o A256823 isok(n) = a8(n) == a9(n); \\ _Michel Marcus_, Sep 15 2019 %Y A256823 Cf. A257378, A257379. %K A256823 nonn,more %O A256823 1,1 %A A256823 _Pierre CAMI_, Apr 24 2015