Well it could be many numbers... if the number is in the hundredths place, it would have to be 15.45-15.49
that's very interesting!! is there more to your question that we can answer?
If it has rational coefients and is a polygon
if a+bi is a root then a-bi is also a root
the roots are -4 and 2+i
so then 2-i must also be a root
if the rots of a poly are r1 and r2 then the factors are
f(x)=(x-r1)(x-r2)
roots are -4 and 2+i and 2-i
f(x)=(x-(-4))(x-(2+i))(x-(2-i))
f(x)=(x+4)(x-2-i)(x-2+i)
expand
f(x)=x³-11x+20
4(1)-1=3
4(2)-1=7
4(3)-1=11
4(4)-1=15
4(5)-1=19