104 articles
Perfect power
A perfect power is a positive integer that can be written as m^k, with m > 1 and k at least 2, such as 4, 8, 9, and 27.
Power of 10
A power of 10 is a number like 100 or 1000, written 10 to the nth power, that underlies decimal notation and the SI metric prefixes.
Power of two
A power of two is a number written as 2 to a whole-number exponent, beginning 1, 2, 4, 8, 16, 32, and important in computing.
Practical number
A practical number is a positive integer such that every integer up to n is a sum of distinct divisors of n; 12 is the classic example.
Primorial
The primorial is the analog of the factorial for primes: the product of the first n primes, or all primes up to n, written n#.
Repunit
A repunit is a whole number whose decimal digits are all 1, such as 11 or 111, with the name coined by Albert H. Beiler in 1966.
Significance of numbers in Judaism
The significance of numbers in Judaism covers symbolic numbers like seven, twelve, and 40, plus gematria, which gives Hebrew letters numerical values, making 18 the value of chai, or life.
Square number
A square number, or perfect square, is an integer that is the product of an integer with itself, such as 0, 1, 4, 9, 16, and 25.
Superior highly composite number
A superior highly composite number is an integer that maximizes the divisor-count ratio d(n)/n^ε for some ε, introduced by Srinivasa Ramanujan in his 1915 memoir on highly composite numbers.
Tetractys (τετρακτύς)
The tetractys (τετρακτύς, Tetraktys) is a triangular figure of ten points in four rows of one, two, three, and four, revered by the Pythagoreans and sworn upon in their oaths.
Triangular number
A triangular number counts objects arranged in an equilateral triangle, equaling the sum 1 + 2 + ... + n; the first few are 0, 1, 3, 6, and 10.
Triangular numbers
A triangular number is the sum of the integers from 1 to n, equal to n(n+1)/2; the sequence begins 0, 1, 3, 6, 10, 15, 21.
Wheat and chessboard problem
The wheat and chessboard problem, also called the rice and chessboard problem, is a mathematical exercise where grains double on each square, totaling 18 quintillion grains across 64 squares.
Zero to the power of zero
Zero to the power of zero, written 0⁰, is the expression with both base and exponent zero, defined as 1 in combinatorics and computing standards but indeterminate in real analysis.