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 A381040 #16 Apr 25 2025 04:31:16 %S A381040 7,9,10,15,21225 %N A381040 Numbers k such that the concatenation of 1, k! and 1 is prime. %C A381040 Also, numbers k such that 10^(A034886(k)+1) + 10k! + 1 is prime. %C A381040 For k >= 5, the foregoing requires that 10^(A034886(k)+1) + 1 has no prime factors <= k. %C A381040 a(6) > 10^5. - _Michael S. Branicky_, Apr 24 2025 %e A381040 The concatenation of 1, 7! and 1 is 150401, which is prime, so 7 is a term. %Y A381040 Cf. A000142, A034886. %Y A381040 Corresponding primes are in A262195. %K A381040 nonn,base %O A381040 1,1 %A A381040 _Michael S. Branicky_, Apr 14 2025