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 A121837 #25 Jun 25 2021 23:13:48
%S A121837 2,9,7,7,17,7,29,17,19,23,23,13,29,79,19,89,97,53,43,347,127,127,149,
%T A121837 29,167,331,379,61,59,167,199,557,107,113,43,191,439,41,263,227,109,
%U A121837 71,227,137,149,409,271,53,157,79,503,103,461,137,587,233,491,73,367,233,449
%N A121837 Least positive j such that Product_{k=1..n} D(k) + j is prime, where D() are the doublets, A020338.
%C A121837 Is every term for n > 2 always prime?
%C A121837 a(159) = 1. - _Michel Marcus_, Jan 07 2021
%C A121837 a(n) = 1 for n = 245 and 702 (using ispseudoprime() in PARI). - _Michel Marcus_, Jan 08 2021
%H A121837 Michel Marcus, <a href="/A121837/b121837.txt">Table of n, a(n) for n = 1..200</a>
%F A121837 a(n) = A013632(A121826(n)). - _Michel Marcus_, Jan 07 2021
%o A121837 (PARI) D(n) = eval(Str(n, n)); \\ A020338
%o A121837 f(n) = prod(k=1, n, D(k)); \\ A121826
%o A121837 a(n) = my(q=f(n)); nextprime(q+1) - q; \\ _Michel Marcus_, Jan 07 2021
%Y A121837 Cf. A013632, A020338, A121826, A151800.
%K A121837 nonn,base
%O A121837 1,1
%A A121837 _Jason Earls_, Aug 28 2006