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A182029
Least odd k > a(n-1) such that 3*k*2^n-1 is a prime number.
1
1, 5, 7, 9, 15, 25, 31, 33, 35, 45, 47, 49, 59, 65, 91, 115, 127, 135, 137, 149, 165, 175, 183, 185, 217, 225, 245, 273, 279, 287, 303, 349, 359, 429, 433, 445, 457, 525, 577, 593, 599, 629, 641, 673, 675, 679, 727, 749, 775, 795, 835, 855, 973, 1049, 1087
OFFSET
1,2
COMMENTS
As n increases a(n)/A000217(n) tends to 0.45.
MATHEMATICA
lok[{n_, a_}]:=Module[{k=a+2, c=3*2^n}, While[!PrimeQ[c*k-1], k+=2]; {n+1, k}]; Drop[NestList[ lok, {1, 1}, 60][[;; , 2]], {2}] (* Harvey P. Dale, Sep 12 2023 *)
CROSSREFS
Cf. A210651.
Sequence in context: A029606 A247283 A050595 * A177941 A029667 A264747
KEYWORD
nonn
AUTHOR
Pierre CAMI, Apr 07 2012
STATUS
approved