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

1,1

Links

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

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

Example

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.

Mathematica

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

Prog

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

Crossrefs

Cf. A042963, A042964, A057812, A237990.

Sequence in context: A275990 A220142 A032649 * A185382 A257065 A066286

Adjacent sequences: A237986 A237987 A237988 * A237990 A237991 A237992

Keyword

nonn,easy

Author

Ivan N. Ianakiev, Feb 16 2014

Status

approved