A237989 Numbers m such that the numbers of primes, even positive integers and odd positive integers less than or equal to m are all odd.

2, 6, 18, 26, 34, 42, 50, 70, 74, 78, 86, 98, 106, 110, 130, 138, 150, 158, 162, 170, 198, 214, 218, 222, 234, 238, 242, 246, 250, 258, 262, 270, 278, 286, 290, 310, 314, 334, 354, 358, 370, 382, 390, 394, 402, 406, 442, 450, 454, 462, 470, 474, 478, 490, 502

Offset: 1

Author

Ivan N. Ianakiev, Feb 16 2014

Keywords

• nonn
• easy

Examples

			A cubic die whose faces are marked with the numbers from 1 to 6 has odd number of sides marked with prime numbers (2, 3 and 5), even integers (2, 4 and 6) and odd integers (1, 3 and 5). Therefore, 6 is in the sequence.
		

Links

• Ivan N. Ianakiev, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A042963, A042964, A057812, A237990.

Programs

Mathematica

Select[Range[2, 1000, 4], OddQ[PrimePi[#]] &] (* Paolo Xausa, Jun 24 2024 *)

PARI

isok(n) = (primepi(n) % 2) && ((n % 4) == 2); \\ Michel Marcus, Mar 12 2014

Formula

Intersection of A042963 (odd number of odd numbers), A042964 (odd number of even numbers), A057812 (odd number of primes). - Michel Marcus, Feb 26 2014