A079111 Numbers n such that 2*n+1 or n itself is prime.

1, 2, 3, 5, 6, 7, 8, 9, 11, 13, 14, 15, 17, 18, 19, 20, 21, 23, 26, 29, 30, 31, 33, 35, 36, 37, 39, 41, 43, 44, 47, 48, 50, 51, 53, 54, 56, 59, 61, 63, 65, 67, 68, 69, 71, 73, 74, 75, 78, 79, 81, 83, 86, 89, 90, 95, 96, 97, 98, 99, 101, 103, 105, 107, 109, 111, 113, 114, 116

Offset: 1

Author

Reinhard Zumkeller, Dec 24 2002

Keywords

• nonn

Comments

Union of A000040 and A005097; complement of A077654.

Programs

PARI

is(n)=isprime(n) || isprime(2*n+1) \\ Charles R Greathouse IV, Jun 13 2017

Formula

a(n) ~ (n log n)/2. - Charles R Greathouse IV, Jun 13 2017