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A320724
Numbers k such that 401*2^k+1 is prime.
0
3, 7, 57, 123, 615, 2103, 2793, 7873, 2088713
OFFSET
1,1
MAPLE
select(k->isprime(401*2^k+1), [$1..1000]); # Muniru A Asiru, Jan 04 2019
MATHEMATICA
Select[Range[1000], PrimeQ[401*2^# + 1] &]
CROSSREFS
Sequence in context: A130294 A321968 A100772 * A259266 A131652 A213734
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 04 2019
EXTENSIONS
a(9) from Jeppe Stig Nielsen, May 30 2020
STATUS
approved