OFFSET
1,1
COMMENTS
If prime(n) is a Mersenne prime exponent then 2^prime(n)-1 is a prime < k*2^prime(n)-1.
LINKS
Pierre CAMI, Table of n, a(n) for n = 1..1000
MAPLE
3*2^2-1=11 prime so a(1)=3.
3*2^3-1=23 prime so a(2)=3.
3*2^5-1=95 composite, 5*2^5-1=159 composite, 7*2^5-1=223 prime so a(3)=7.
MATHEMATICA
a249806[n_Integer] := Catch[Module[{k}, For[k = 3, k < 10^5, k += 2, If[PrimeQ[k*2^Prime[n] - 1], Throw[k], 0]]]]; a249806 /@ Range[120] (* Michael De Vlieger, Nov 11 2014 *)
PROG
(PFGW & SCRIPT)
SCRIPT
DIM j, 0
DIM k
DIM n
DIMS t
OPENFILEOUT myf, a(n).txt
LABEL loop1
SET j, j+1
IF j>1000 THEN END
SET k, p(j)
SET n, 1
LABEL loop2
SET n, n+2
SETS t, %d, %d, %d\,; j; k; n
PRP n*2^k-1, t
IF ISPRP THEN GOTO a
GOTO loop2
LABEL a
WRITE myf, t
GOTO loop1
(PARI) s=[]; forprime(p=2, 500, k=3; q=2^p; while(!ispseudoprime(k*q-1), k+=2); s=concat(s, k)); s \\ Colin Barker, Nov 06 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Nov 06 2014
STATUS
approved