The endosperm nucleus is
Haploid
Diploid
Triploid
Tetraploid
As we learn
Endosperm -
The primary endosperm cell divides repeatedly and forms a triploid endosperm tissue. The cells of this tissue are filled with reserve food materials and are used for the nutrition of the developing embryo
-2n (Polar nuclei) + n (Male gamete) = 3n (PEN)