quasiperfect
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Quasiperfect number — In mathematics, a quasiperfect number is a theoretical natural number n for which the sum of all its divisors (the divisor function σ ( n )) is equal to 2 n + 1. Quasiperfect numbers are abundant numbers. No quasiperfect numbers have been found… … Wikipedia
Prime number — Prime redirects here. For other uses, see Prime (disambiguation). A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A natural number greater than 1 that is not a prime number is… … Wikipedia
Perfect number — In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself (also known as its aliquot sum). Equivalently, a perfect… … Wikipedia
Divisor — divisible redirects here. For divisibility of groups, see Divisible group. For the second operand of a division, see Division (mathematics). For divisors in algebraic geometry, see Divisor (algebraic geometry). For divisibility in the ring theory … Wikipedia
Composite number — A composite number is a positive integer which has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number. So, if n > 0 is an integer and… … Wikipedia
Unsolved problems in mathematics — This article lists some unsolved problems in mathematics. See individual articles for details and sources. Millennium Prize Problems Of the seven Millennium Prize Problems set by the Clay Mathematics Institute, the six ones yet to be solved are:… … Wikipedia
Highly composite number — This article is about numbers having many divisors. For numbers factorized only to powers of 2, 3, 5 and 7 (also named 7 smooth numbers), see Smooth number. A highly composite number (HCN) is a positive integer with more divisors than any… … Wikipedia
Multiply perfect number — In mathematics, a multiply perfect number (also called multiperfect number or pluperfect number) is a generalization of a perfect number. For a given natural number k, a number n is called k perfect (or k fold perfect) if and only if the sum of… … Wikipedia
Abundant number — In mathematics, an abundant number or excessive number is a number n for which σ ( n ) > 2 n . Here σ ( n ) is the sum of divisors function: the sum of all positive divisors of n , including n itself. The value σ ( n ) − 2 n is called the… … Wikipedia
Deficient number — In number theory, a deficient number or defective number is a number n for which the sum of divisors σ(n)<2n, or, equivalently, the sum of proper divisors (or aliquot sum) s(n)<n. The value 2n − σ(n) (or n − s(n)) is… … Wikipedia
