OFFSET
1,2
COMMENTS
Numbers with the same number of primes appearing along the main diagonal and along the main antidiagonal of an n X n square array whose elements are the numbers from 1..n^2, listed in increasing order by rows (see example).
EXAMPLE
5 is in the sequence since there are 3 primes along the main diagonal and 3 primes along the main antidiagonal of the 5 X 5 array below.
[1 2 3 4 5]
[6 7 8 9 10]
[11 12 13 14 15]
[16 17 18 19 20]
[21 22 23 24 25]
MATHEMATICA
q[k_] := Sum[Boole @ PrimeQ[k*j - j + 1] - Boole @ PrimeQ[k*(j - 1) + j], {j, 1, k}] == 0; Select[Range[1000], q] (* Amiram Eldar, Dec 28 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Dec 28 2021
EXTENSIONS
More terms from Amiram Eldar, Dec 28 2021
STATUS
approved