OFFSET
1,2
COMMENTS
Conjecture: there is no "Riesel" number of the form 4^n-1; that is, a(n) exists for all n.
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..2500
EXAMPLE
(4^1-1)*2^1-1=5 prime so a(1)=1.
(4^2-1)*2^2-1=59 prime so a(2)=2.
MATHEMATICA
sk[n_]:=Module[{k=n, c=4^n-1}, While[!PrimeQ[c*2^k-1], k++]; k]; Array[sk, 70] (* Harvey P. Dale, Jul 30 2020 *)
PROG
PFGW & SCRIPTIFY
SCRIPT
DIM k
DIM n, 0
DIMS tt
OPENFILEOUT myf, a(n).txt
LABEL a
SET n, n+1
IF n>2500 THEN END
SET k, n-1
LABEL b
SET k, k+1
SETS tt, %d, %d\,; n; k
PRP (4^n-1)*2^k-1, tt
IF ISPRP THEN GOTO c
GOTO b
LABEL c
WRITE myf, tt
GOTO a
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Oct 03 2013
STATUS
approved