(n²+n+4)/(n+1)
daca n∈Z,ca fractia sa ∈Z ⇒
[n(n+1)+4]/(n+1)=n(n+1)/(n+1) +4/(n+1)=
n+ 4/(n+1)
deoarece din ipoteza n ∈Z trebuie sa demonstram ca 4/(n+1)∈Z
inseamna ca n+1=D4
D4={-4-2-1,1,2,4}
n+1=-4 ⇒ n=-5
n+1=-2 ⇒n=-3
n+1=-1 ⇒n=-2
n+1=1 ⇒n=0
n+1=2 ⇒n=1
n+1=4 ⇒n=3
n={-5,-3,-2,0,1,3}
