A145690 a(n) = least k such that 3*2^n*(3*2^n-k)-1 is prime

1, 1, 3, 2, 4, 1, 8, 3, 11, 3, 12, 9, 3, 10, 2, 4, 6, 13, 3, 7, 2, 6, 11, 4, 2, 1, 7, 8, 4, 3, 3, 18, 16, 13, 21, 17, 51, 10, 23, 9, 24, 27, 9, 8, 18, 13, 6, 23, 24, 3, 21, 18, 28, 11, 3, 54, 9, 5, 41, 17, 19

Offset

1,3

Comments

As n increases, Sum_{i=1..n} a(n) tends to (2*log(2)/3)*n*(n+1)/2.

Links

Pierre CAMI, Table of n, a(n) for n = 1..4001

Example

3*2*(3*2-1)-1=29 prime so a(1)=1 3*2^2*(3*2^2-1)-1=131 prime so a(2)=1

Crossrefs

Sequence in context: A144868 A134029 A117623 * A259053 A161911 A139583

Adjacent sequences: A145687 A145688 A145689 * A145691 A145692 A145693

Keyword

nonn

Author

Pierre CAMI, Oct 16 2008

Status

approved