the ruse of inflicting an injury upon oneself to win the trust of one's enemy (one of the Thirty-Six Stratagems of ancient China)

spectrometer

(computing, input devices) alphanumerics, alphanumeric characters (as opposed to kana or kanji)

a male given name

a male given name

a male given name

a composite number

(number theory) amicable numbers, two different numbers related in such a way that the sum of the proper divisors of each is equal to the other number.

(number theory) perfect number, a positive integer that is equal to the sum of its positive divisors, excluding the number itself

(number theory) deficient number, a number for which the sum of proper divisors is less than that number