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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

All terms are odd.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

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 * A170819 A140211 A248101

Adjacent sequences:  A345465 A345466 A345467 * A345469 A345470 A345471

KEYWORD

nonn

AUTHOR

Robert Israel, Jun 20 2021

STATUS

approved

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Last modified January 20 00:34 EST 2022. Contains 350467 sequences. (Running on oeis4.)