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A345468
a(n) is the least number k such that k^2+4*n is prime.
2
1, 3, 1, 1, 3, 7, 1, 3, 1, 1, 3, 5, 1, 9, 1, 3, 9, 1, 5, 3, 5, 1, 3, 1, 1, 3, 1, 1, 9, 11, 5, 3, 5, 1, 3, 7, 1, 9, 1, 9, 3, 5, 1, 9, 1, 3, 3, 1, 1, 9, 5, 5, 9, 5, 3, 3, 1, 1, 9, 1, 5, 3, 5, 1, 3, 7, 1, 3, 1, 1, 3, 5, 1, 15, 7, 3, 3, 1, 1, 9, 5, 3, 15, 1, 3, 3, 1, 1, 21, 7, 3, 9, 1, 5, 3, 5, 1, 3
OFFSET
1,2
COMMENTS
All terms are odd.
LINKS
EXAMPLE
a(5) = 3 because 3^2+4*5 = 29 is prime but 1^2+4*5 and 2^2+4*5 are not.
MAPLE
f:= proc(n) local k, m;
m:= 4*n;
for k from 1 by 2 do
if isprime(k^2+m) then return k fi
od
end proc:
map(f, [$1..200]);
CROSSREFS
Cf. A345469.
Sequence in context: A058735 A107294 A161788 * A351518 A170819 A140211
KEYWORD
nonn
AUTHOR
Robert Israel, Jun 20 2021
STATUS
approved