A276660 Primes of the form p*2^k - 1 where p is an odd prime and k >= 0.

2, 5, 11, 13, 19, 23, 37, 43, 47, 61, 67, 73, 79, 103, 151, 157, 163, 191, 193, 211, 223, 271, 277, 283, 313, 331, 367, 383, 397, 421, 457, 463, 487, 523, 541, 547, 607, 613, 631, 661, 673, 691, 733, 751, 757, 787, 823, 877, 907, 991, 997, 1051, 1087, 1093, 1123

Offset: 1

Author

Juri-Stepan Gerasimov, Sep 11 2016

Keywords

• nonn

Examples

			2 is in this sequence because 3*2^0 - 1 = 2 is prime.
5 is in this sequence because 3*2^1 - 1 = 5 is prime.
11 is in this sequence because 3*2^2 - 1 = 11 is prime.
		

Crossrefs

Essentially the same as A192869 and A206581.

Cf. A038550, A058500.

Programs

PARI

is(n)=isprime((n+1)>>valuation(n+1,2)) && isprime(n) \\ Charles R Greathouse IV, Sep 11 2016

Formula

a(n) >> n (log n)^2. - Charles R Greathouse IV, Sep 11 2016