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URL: https://oeis.org/A210651

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A210651
a(n)=least odd number k such that 3*k*2^n-1 is a prime number.
4
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
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
(PFGW)
' 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
KEYWORD
nonn
AUTHOR
Pierre CAMI, Mar 27 2012
STATUS
approved