Hemiperfect數係指一個正整數嘅過剩指數係半整數，亦即係奇數除以2，過剩指數（abundancy index）就係除數函數（包括本身嘅所有正因數嘅和）除以佢自己嘅結果。
The hemiperfect number is a positive integer in which the excess exponent is a half integer, i.e. an odd number divided by 2, and the excess index is the result of dividing the divisor function (including the sum of all its positive factors) by itself.