6,052 articles
2
2, or two, is the natural number after 1 and the unique even prime, with exactly two divisors, making it the base of the binary system in computing.
2-category
A 2-category is a category-like structure with objects, 1-morphisms, and 2-morphisms between parallel morphisms; its weak form is the bicategory, introduced by Jean Bénabou in 1968.
2-opt
2-opt is a local search move for the traveling salesman problem that deletes two edges of a tour and reconnects the paths the other way, shortening the tour.
2-satisfiability
2-satisfiability (2-SAT) is the problem of deciding whether a Boolean formula whose clauses each contain exactly two literals has a satisfying truth assignment, solvable in linear time.
2,147,483,647
2,147,483,647, the maximum value of a signed 32-bit integer, is the prime number equal to 2^31 − 1 and the eighth Mersenne prime, proved prime by Leonhard Euler.
20 (number)
20 (twenty, Roman numeral XX) is the natural number following 19 and preceding 21, the atomic number of calcium and the base of vigesimal counting systems used by the Maya.
22 (number)
22 (twenty-two) is the even composite number following 21, the product of 2 and 11, the atomic number of titanium, and the numerator of the approximation 22/7 to pi.
23 (number)
23 (twenty-three) is the prime number following 22 and preceding 24, known for the 23 pairs of chromosomes in a human cell and the 23 enigma, a coincidence cult.
23 enigma
The 23 enigma is the belief that the number 23 recurs in significant events more than chance allows, originating with William S. Burroughs and popularized by Robert Anton Wilson.
24-cell
The 24-cell is a regular convex 4-polytope with 24 octahedral cells, 24 vertices, and 96 edges, the unique self-dual regular four-dimensional polytope, classified by Ludwig Schläfli.
25 (number)
25, or twenty-five, is the natural number following 24 and preceding 26; it is the square of 5, the smallest multi-digit automorphic number, and the atomic number of manganese.
26 (number)
26 (twenty-six) is the even composite number between 25 and 27, the only integer directly between a perfect square and a perfect cube, and the atomic number of iron.
27 (number)
27 (twenty-seven) is the natural number after 26, a perfect cube equal to 3³, the atomic number of cobalt, and the number of lines on every smooth cubic surface.
28 (number)
28 (twenty-eight) is the even composite number that is the second perfect number, after 6, its proper divisors 1, 2, 4, 7, and 14 summing to 28.
29 (number)
29 (twenty-nine) is the natural number following 28 and preceding 30, the tenth prime number, also a Sophie Germain prime, Pell number, Lucas number, and sum of two squares.
3
3 (three) is the smallest odd prime number, the only prime one more than another prime (2), and a member of the Fibonacci and triangular number sequences.
3-manifold
A 3-manifold is a topological space in which every point has a neighborhood like three-dimensional Euclidean space; the field culminated in Perelman's proof of the Poincaré conjecture.
3-satisfiability
3-satisfiability, or 3-SAT, is the NP-complete problem of deciding whether a Boolean formula whose clauses each contain three literals has a truth assignment satisfying every clause.
3-sphere
The 3-sphere, also called the three-sphere, is the set of points in four-dimensional space at distance 1 from the origin, the basic closed 3-manifold of topology.
30 (number)
30 is the natural number after 29, an even composite number whose factorization 2 × 3 × 5 makes it the smallest sphenic number and the third primorial.
32 (number)
32 (thirty-two) is the fifth power of two, a number that shapes computing through 32-bit processors and IEEE single-precision floats, and equals the atomic number of germanium.
33 (number)
33 is the natural number after 32, an odd composite equal to 3 × 11, the atomic number of arsenic, and the count of vertebrae in the human spine.
35 (number)
35 (thirty-five) is an odd semiprime, the natural number following 34 and preceding 36, the fifth tetrahedral and pentagonal number, and the atomic number of bromine.
36 (number)
36 is the natural number equal to the square of 6, the eighth triangular number, the atomic number of krypton, and the number of inches in a yard.
37 (number)
37 (thirty-seven) is the twelfth prime number. It divides 111, is the first irregular prime, and is the number people most often give as a "random" choice.
3D modeling
3D modeling is the construction of a digital representation of an object's shape and appearance, built by hand, captured by scanning, or generated procedurally, feeding games, film, engineering, and 3D printing.
3D projection
3D projection, also called graphical projection, is any method for representing a 3D object on a 2D surface by mapping its points onto a projection plane.
4 (number)
4 (four) is the natural number after 3 and before 5, the smallest positive composite number and the first even perfect square, 4 = 2 squared.
4-polytope
A 4-polytope, or polychoron, is a four-dimensional polytope bounded by three-dimensional cells, like a polyhedron bounded by faces; exactly six are regular and convex, including the tesseract and the 24-cell.
40 (number)
40 (forty) is the natural number following 39 and preceding 41, written XL in Roman numerals and one of the most frequent numbers in the Bible.