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 A261459 #19 Jun 07 2023 08:49:09
%S A261459 1,3,4,5,6,10,254,410,751,1101,2488,3476,14124,20060
%N A261459 Numbers k such that the concatenation of k 1's, the digits of k^2 + k + 1, and k 1's is prime.
%C A261459 Numbers k that generate the terms in A263299.
%C A261459 a(13) > 10000 if it exists. - _Chai Wah Wu_, Oct 22 2015
%o A261459 (Python)
%o A261459 from gmpy2 import is_prime
%o A261459 A261459_list = [k for k in range(10**3) if is_prime(int('1'*k+str(k*(k+1)+1)+'1'*k))]
%o A261459 (PARI) for(n=1, 1e3, if(isprime(eval(Str((10^n - 1)/9, n^2 + n + 1, (10^n - 1)/9))), print1(n", "))); \\ _Altug Alkan_, Oct 20 2015
%Y A261459 Cf. A263299.
%K A261459 nonn,base,more
%O A261459 1,2
%A A261459 _Chai Wah Wu_, Oct 19 2015
%E A261459 a(13)-a(14) from _Michael S. Branicky_, Jun 06 2023