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