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 A344349 #14 Jun 17 2022 13:43:41
%S A344349 0,2,3,2,3,2,6,2,3,3,6,3,7,4,7,6,6,4,10,2,8,7,9,4,11,5,10,8,11,4,17,3,
%T A344349 10,10,12,9,16,4,10,11,14,6,21,7,11,10,16,8,19,6,19,13,17,5,25,10,19,
%U A344349 10,16,9,27,7,16,13,16,13,31,9,18,14,27,10,26,10,20,19,17,12,30
%N A344349 Number of primes along the main antidiagonal of the n X n square array whose elements are the numbers from 1..n^2, listed in increasing order by rows.
%F A344349 a(n) = Sum_{k=1..n} c(n*k-k+1), where c is the prime characteristic.
%e A344349 [1 2 3 4 5]
%e A344349 [1 2 3 4] [6 7 8 9 10]
%e A344349 [1 2 3] [5 6 7 8] [11 12 13 14 15]
%e A344349 [1 2] [4 5 6] [9 10 11 12] [16 17 18 19 20]
%e A344349 [1] [3 4] [7 8 9] [13 14 15 16] [21 22 23 24 25]
%e A344349 ------------------------------------------------------------------------
%e A344349 n 1 2 3 4 5
%e A344349 ------------------------------------------------------------------------
%e A344349 a(n) 0 2 3 2 3
%e A344349 ------------------------------------------------------------------------
%e A344349 primes {} {2,3} {3,5,7} {7,13} {5,13,17}
%e A344349 ------------------------------------------------------------------------
%t A344349 Table[Sum[PrimePi[n*k - k + 1] - PrimePi[n*k - k], {k, n}], {n, 100}]
%Y A344349 Cf. A010051, A221490, A344316 (primes along border).
%K A344349 nonn
%O A344349 1,2
%A A344349 _Wesley Ivan Hurt_, May 15 2021