A261459 Numbers k such that the concatenation of k 1's, the digits of k^2 + k + 1, and k 1's is prime.
1, 3, 4, 5, 6, 10, 254, 410, 751, 1101, 2488, 3476, 14124, 20060
Offset: 1
Crossrefs
Cf. A263299.
Programs
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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
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Python
from gmpy2 import is_prime A261459_list = [k for k in range(10**3) if is_prime(int('1'*k+str(k*(k+1)+1)+'1'*k))]
Extensions
a(13)-a(14) from Michael S. Branicky, Jun 06 2023
Comments