A350328 Numbers k such that pi(k) = Sum_{i=1..k} pi(k*(i-1)+i) - pi(k*(i-1)+i-1).

1, 5, 21, 23, 25, 33, 81, 85, 115, 127, 141, 164, 253, 273, 283, 285, 291, 343, 385, 441, 471, 495, 505, 565, 577, 711, 807, 921, 1107, 1977, 2175, 2437, 2941, 2943, 3381, 4117, 5541, 6531, 7075, 7497, 8193, 8325, 8923

Offset: 1

Author

Wesley Ivan Hurt, Dec 24 2021

Keywords

• nonn

Comments

Numbers with the same number of primes on the top row and along the main diagonal of an n X n square array whose elements are the numbers from 1..n^2, listed in increasing order by rows (see example).

Examples

			5 is in the sequence since there are 3 primes in the top row and 3 primes along the main diagonal 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]
		

Crossrefs

Cf. A000720 (pi), A221490.

Formula

Numbers k such that A000720(k) = A221490(k).