OFFSET
1,3
COMMENTS
The absolute value of a(1) through a(3) and a(5), are squares. None of the absolute values of a(1) through a(8) are themselves squarefree.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..898
EXAMPLE
a(2) = -1 =
|1 2|
|3 5|.
a(3) = -4 =
|.1..2..3|
|.5..6..7|
|10.11.13|.
MATHEMATICA
s = Select[Range[1500], SquareFreeQ]; n = Length[s]; m = Floor[Sqrt[n]]; seq = {}; Do[mat = Partition[s[[1 ;; k^2]], k]; AppendTo[seq, Det[mat]], {k, 1, m}]; seq (* Amiram Eldar, Aug 23 2019 *)
Module[{nn=30, sqfr}, sqfr=Select[Range[2 nn^2], SquareFreeQ]; Table[Det[ Partition[ Take[ sqfr, n^2], n]], {n, nn}]] (* Harvey P. Dale, Jul 09 2022 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Jonathan Vos Post, May 27 2006
EXTENSIONS
More terms from Amiram Eldar, Aug 23 2019
STATUS
approved