  In this paper we study practical numbers of some special forms. For any
integers $b\ge0$ and $c>0$, we show that if $n^2+bn+c$ is practical for some
integer $n>1$, then there are infinitely many nonnegative integers $n$ with
$n^2+bn+c$ practical. We also prove that there are infinitely many practical
numbers of the form $q^4+2$ with $q$ practical, and that there are infinitely
many practical Pythagorean triples $(a,b,c)$ with $\gcd(a,b,c)=6$ (or
$\gcd(a,b,c)=4$).
