OFFSET
1,2
COMMENTS
Called "circle" because drawing a circle on the complex plane centered at 0 with radius n encloses the integers (with the exception of 0) that will be considered in computing a(n).
All terms of this sequence are purely real numbers.
EXAMPLE
a(1) = 1 * i * -1 * -i = -1. (Note that numbers like -1 + i are ignored here).
a(5) = 5 * (4 + 3i) * (3 + 4i) * 5i * (-3 + 4i) * (-4 + 3i) * ... (Note that the absolute value of numbers like 4 + 3i is precisely 5).
MATHEMATICA
Table[Times@@Select[ReplaceAll[Flatten[Table[a + b I, {a, -n, n}, {b, -n, n}]], 0 -> 1], Abs[#] <= n &], {n, 10}]
CROSSREFS
KEYWORD
sign
AUTHOR
Alonso del Arte, Jan 09 2012
STATUS
approved