Let <i>f(x) =  a<sub>n</sub>x<sup>n</sup> +   a<sub>n -1</sub> x<sup>n-1</sup> + ... +  a<sub>0</sub></i>  belong to  <i>Z[x]</i>.
If there is a prime <i>p</I> such that <i>p</i> does not divide <i> a<sub>n</sub>, p</i>  divides <i> a<sub>n -1</sub>, . . . , p</i> divides <i> 
a<sub>0</sub></I> and <i>p<sup>2</sup></I> does not divide <i> a<sub>0</sub>,</i>
then <i>f(x)</i> is irreducible over <i>Q.</I>