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A145690 a(n) = least k such that 3*2^n*(3*2^n-k)-1 is prime 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
As n increases, Sum_{i=1..n} a(n) tends to (2*log(2)/3)*n*(n+1)/2.
LINKS
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
KEYWORD
nonn
AUTHOR
Pierre CAMI, Oct 16 2008
STATUS
approved

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Last modified June 15 22:50 EDT 2024. Contains 373412 sequences. (Running on oeis4.)