A192868 Thin numbers: odd numbers k > 1 such that k+1 is a prime times a power of two.

3, 5, 7, 9, 11, 13, 15, 19, 21, 23, 25, 27, 31, 33, 37, 39, 43, 45, 47, 51, 55, 57, 61, 63, 67, 73, 75, 79, 81, 85, 87, 91, 93, 95, 103, 105, 111, 115, 117, 121, 123, 127, 133, 135, 141, 145, 147, 151, 157, 159, 163, 165, 171, 175, 177, 183, 187, 191, 193

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Kevin A. Broughan and Zhou Qizhi, Flat primes and thin primes, Bulletin of the Australian Mathematical Society, Vol. 82, No. 2 (2010), pp. 282-292, alternative link.

Formula

a(n) ~ n log n.

Mathematica

Select[Range[3, 200, 2], (r = (# + 1)/2^IntegerExponent[# + 1, 2]) == 1 || PrimeQ[r] &] (* Amiram Eldar, Aug 30 2020 *)

Prog

(PARI) is(n)=n%2&&(isprime((n+1)>>valuation(n+1, 2)) || n+1 == 1<<valuation(n+1, 2))&&n>1

Crossrefs

Cf. A192869.

Sequence in context: A204458 A192861 A333854 * A283553 A081110 A143449

Adjacent sequences: A192865 A192866 A192867 * A192869 A192870 A192871

Keyword

nonn

Author

Charles R Greathouse IV, Jul 11 2011

Status

approved