实际数（practical number）是指一正整数n有许多因数，所有小于n的正整数都可以用数个n的相异真因数和表示。例如12的真因数有1, 2, 3, 4及6，而1至11的数字中有几个不是12的真因数，但都可以表示为数个相异真因数的和：5=3+2, 7=6+1, 8=6+2, 9=6+3, 10=6+3+1及11=6+3+2。

以下是实际数的列表（OEIS中的数列A005153）：1, 2, 4, 6, 8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 48, 54, ....

In number theory, a practical number or panarithmic number is a positive integer n such that all smaller positive integers can be represented as sums of distinct divisors of n. For example, 12 is a practical number because all the numbers from 1 to 11 can be expressed as sums of its divisors 1, 2, 3, 4, and 6: as well as these divisors themselves, we have 5 = 3 + 2, 7 = 6 + 1, 8 = 6 + 2, 9 = 6 + 3, 10 = 6 + 3 + 1, and 11 = 6 + 3 + 2.