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A227897 Numbers k such that k^2 + 2 is not squarefree. 3
4, 5, 13, 14, 19, 22, 23, 24, 31, 32, 40, 41, 49, 50, 58, 59, 63, 67, 68, 71, 76, 77, 85, 86, 94, 95, 102, 103, 104, 112, 113, 121, 122, 130, 131, 139, 140, 148, 149, 157, 158, 166, 167, 175, 176, 184, 185, 193, 194, 202, 203, 211, 212, 218, 220, 221, 223, 229 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Primes dividing k^2 + 2 at least twice are in A033200. - Charles R Greathouse IV, Oct 14 2013
LINKS
FORMULA
{k: k^2 + 2 is in A013929}.
EXAMPLE
4 is in the sequence because 4^2 + 2 = 18 = 2 * 3^2, which is not squarefree.
5 is in the sequence because 5^2 + 2 = 27 = 3^3, which is not squarefree.
6 is not in the sequence because 6^2 + 2 = 38 = 2 * 19, which is squarefree.
MATHEMATICA
Select[Range[300], ! SquareFreeQ[#^2 + 2] &] (* T. D. Noe, Oct 14 2013 *)
(* The following works in Mathematica versions prior to 6.0 *) Select[Range[250], MoebiusMu[#^2 + 2] == 0 &] (* Alonso del Arte, Oct 14 2013 *)
PROG
(PARI) is(n)=!issquarefree(n^2+2) \\ Charles R Greathouse IV, Oct 14 2013
CROSSREFS
Sequence in context: A102703 A283483 A288755 * A156638 A098868 A087882
KEYWORD
nonn,easy
AUTHOR
Gerasimov Sergey, Oct 14 2013
STATUS
approved

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Last modified March 28 21:57 EDT 2024. Contains 371254 sequences. (Running on oeis4.)