A344781 Numbers k such that A070313(k) = 2^k - (2*k+1) is a prime number.

4, 7, 8, 28, 32, 81, 669, 1108, 1699, 1839, 2319, 9566, 14866, 30855, 35932, 56048, 70915, 72578

Offset: 1

Author

Amiram Eldar, May 28 2021

Keywords

• nonn
• more

Comments

The corresponding primes are 7, 113, 239, 268435399, 4294967231, 2417851639229258349412189, ...

If k is a term of this sequence then 2^(k-1)*(2^k-(2*k+1)) is a term of A056075 (see Farideh Firoozbakht's comment in A056075).

Examples

			4 is a term since 2^4 - (2*4+1) = 16 - 9 = 7 is a prime.
7 is a term since 2^7 - (2*7+1) = 128 - 15 = 113 is a prime.
		

Crossrefs

Cf. A056075, A070313.

Programs

Mathematica

Select[Range[2400], PrimeQ[2^# - 2*# - 1] &]

Extensions

a(16)-a(18) from Michael S. Branicky, May 07 2024