A210651 a(n)=least odd number k such that 3*k*2^n-1 is a prime number

1, 1, 1, 1, 5, 1, 1, 9, 15, 5, 1, 29, 3, 5, 3, 15, 5, 1, 17, 19, 3, 11, 23, 13, 19, 19, 7, 9, 15, 71, 5, 19, 49, 1, 11, 15, 7, 1, 21, 39, 5, 11, 1, 19, 55, 11, 71, 39, 23, 29, 7, 61, 49, 15, 1, 11, 17, 37, 15, 31, 23, 19, 3, 1, 33, 21, 37, 21, 17, 9, 41, 43, 5, 7, 25, 1, 19, 37, 23, 5, 27, 5, 37, 31, 15, 85, 67, 43, 79, 77

Offset

1,5

Links

Pierre CAMI, Table of n, a(n) for n = 1..7725

Maple

A210651 := proc(n)
        for k from 1 by 2 do
                if isprime(3*k*2^n-1) then
                        return k;
                end if;
        end do:
end proc: # R. J. Mathar, Mar 29 2012

Prog

PFGW64 and SCRIPTIFY from Primeform group
Command: pfgw64 -f in.txt
in.txt file :
SCRIPT
DIM nn, 0
DIM kk
DIMS tt
OPENFILEOUT myfile, a(n).txt
LABEL loopn
SET nn, nn+1
IF nn>7725 THEN END
SET kk, -1
LABEL loopk
SET kk, kk+2
SETS tt, %d, %d\,; nn; kk
PRP 3*kk*2^nn-1, tt
IF ISPRP THEN GOTO a
IF ISPRIME THEN GOTO a
GOTO loopk
LABEL a
WRITE myfile, tt
GOTO loopn

Crossrefs

Cf. A126717.

Sequence in context: A081578 A184883 A279003 * A255831 A363970 A356113

Adjacent sequences: A210648 A210649 A210650 * A210652 A210653 A210654

Keyword

nonn

Author

Pierre CAMI, Mar 27 2012

Status

approved