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A252733 Smallest number k such that (k^2)*2^(2*n+1)-1 is a prime number. 2
2, 1, 1, 1, 4, 2, 1, 2, 1, 1, 3, 5, 8, 4, 2, 1, 7, 5, 10, 5, 6, 3, 19, 71, 46, 23, 14, 7, 4, 2, 1, 3, 15, 13, 38, 19, 10, 5, 28, 14, 7, 8, 4, 2, 1, 11, 14, 7, 6, 3, 8, 4, 2, 1, 3, 54, 27, 17, 11, 16, 8, 4, 2, 1, 38, 19, 52, 26, 13, 15, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

If k=1 then 2*n+1 is a Mersenne exponent.

LINKS

Pierre CAMI, Table of n, a(n) for n = 0..2500

EXAMPLE

2*2^1-1=3 prime so a(0)=2.

1*2^3-1=7 prime so a(1)=1.

1*2^5-1=31 prime so a(2)=1.

MATHEMATICA

Table[k=1; While[Not[PrimeQ[k^2*2^(2*n+1)-1]], k++]; k, {n, 0, 100}] (* Vaclav Kotesovec, Dec 21 2014 *)

PROG

(PFGW & SCRIPT)

SCRIPT

DIM n, 0

DIM k

OPENFILEOUT myf, a(n).txt

LABEL loop1

SET n, n+1

SET k, 0

LABEL loop2

SET k, k+1

PRP k^2*2^(2*n+1)-1

IF ISPRP THEN GOTO a

GOTO loop2

LABEL a

WRITE myf, k

GOTO loop1

CROSSREFS

Sequence in context: A297404 A235388 A294897 * A181876 A131505 A100092

Adjacent sequences:  A252730 A252731 A252732 * A252734 A252735 A252736

KEYWORD

nonn

AUTHOR

Pierre CAMI, Dec 21 2014

STATUS

approved

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Last modified September 24 22:46 EDT 2021. Contains 347651 sequences. (Running on oeis4.)