The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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