Categories: Integers A prime number p is called a Sophie Germain prime if 2p + 1 is also prime. ... Amicable numbers are two numbers so related that the sum of the proper divisors of the one is equal to the other, unity being considered as a proper divisor but not the number itself. ... A factorial prime is a number that is one less or one more than a factorial and is also a prime number. ... Five thousand (5000) is the natural number following 4999 and preceding 5001. ... A highly composite number is a positive integer which has more divisors than any positive integer below it. ... Numerology is the study of the purported mystical relationship between numbers and the character or action of physical objects and living things. ... A centered octagonal number is a centered figurate number that represents an octagon with a dot in the center and all other dots surrounding the center dot in successive octagonal layers. ... A triangular number is a number that can be arranged in the shape of an equilateral triangle. ... In mathematics, a Kaprekar number is a number that, in a given base, when squared, can be split into two numbers with the same number of digits as the original number which add up to the original number again. ... A decagonal number is a figurate number that represents a decagon. ... A safe prime is a prime number of the form 2p + 1, where p is also a prime. ... A cuban prime is a prime number that is a solution to one of two different specific equations involving third powers of x and y. ... A centered heptagonal number is a centered figurate number that represents a heptagon with a dot in the center and all other dots surrounding the center dot in successive heptagonal layers. ... A nonagonal number or enneagonal number is a figurate number that represents a nonagon. ... In number theory, a branch of mathematics, a highly cototient number k is an integer that has more solutions to the equation x - φ(x) = k, where φ is Eulers totient function, than any integer below it, with the exception of 1. ... The magic constant of a magic square, an n-by-n matrix, is defined such that the sum of any row, column or main diagonal yields the same result, denoted M2(n). ... In mathematics, a magic square of order n is an arrangement of n² numbers in a square, such that the n numbers in all rows, all columns, and both diagonals sum to the same constant. ... One of the 12 unique solutions The eight queens puzzle is the problem of putting eight chess queens on an 8×8 chessboard such that none of them is able to capture any other using the standard chess queens moves. ... An octahedral number is a figurate number that represents an octahedron, or two pyramids placed together, one upside-down underneath the other. ... A tetrahedral number, or triangular pyramidal number, is a figurate number that represents a pyramid with a base and three sides, that is, a tetrahedron. ... A super-Poulet number is a Poulet number whose every divisor d divides 2d - 2. ... A pyramidal number, or square pyramidal number, is a figurate number that represents a pyramid with a base and four sides. ... In mathematics, the Fibonacci numbers form a sequence defined recursively by: In words: you start with 0 and 1, and then produce the next Fibonacci number by adding the two previous Fibonacci numbers. ... A pentagonal pyramidal number is a number equal to the sum of the first few pentagonal numbers. ... A Zeisel number is a square-free integer k with at least three prime factors which fall into the pattern where a and b are fixed constants and x is the index number of each prime factor in the factorization, sorted from lowest to highest. ... In mathematics, the Fibonacci numbers form a sequence defined recursively by: In words: you start with 0 and 1, and then produce the next Fibonacci number by adding the two previous Fibonacci numbers. ... A Motzkin number for a given number n is the number of different ways of drawing non-intersecting chords on a circle between n points. ... A chiliagonal number is a number that can be arranged to form a chiliagon. ...