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

Offset

1,1

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).

Links

Table of n, a(n) for n=1..15.

Example

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.

Mathematica

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

Crossrefs

Cf. A056075, A070313.

Sequence in context: A295325 A239290 A057464 * A160629 A093105 A141669

Adjacent sequences: A344778 A344779 A344780 * A344782 A344783 A344784

Keyword

nonn,more

Author

Amiram Eldar, May 28 2021

Status

approved