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The smallest integer m > 1 such that p n # + m is a prime number, where the primorial p n # is the product of the first n prime numbers. A005235 Semiperfect numbers
The 4-partition problem is a variant in which S contains n = 4 m integers, the sum of all integers is , and the goal is to partition it into m quadruplets, all with a sum of T. It can be assumed that each integer is strictly between T/5 and T/3.
The Delannoy number D(3, 3) equals 63. The following figure illustrates the 63 Delannoy paths from (0, 0) to (3, 3): The following figure illustrates the 63 Delannoy paths from (0, 0) to (3, 3): The subset of paths that do not rise above the SW–NE diagonal are counted by a related family of numbers, the Schröder numbers .
Lucas numbers have L 1 = 1, L 2 = 3, and L n = L n−1 + L n−2. Primefree sequences use the Fibonacci recursion with other starting points to generate sequences in which all numbers are composite. Letting a number be a linear function (other than the sum) of the 2 preceding numbers.
In particular F n contains all of the members of F n−1 and also contains an additional fraction for each number that is less than n and coprime to n. Thus F 6 consists of F 5 together with the fractions 1 / 6 and 5 / 6 . The middle term of a Farey sequence F n is always 1 / 2 , for n > 1.
Cubic reciprocity is a collection of theorems in elementary and algebraic number theory that state conditions under which the congruence x 3 ≡ p (mod q) is solvable; the word "reciprocity" comes from the form of the main theorem, which states that if p and q are primary numbers in the ring of Eisenstein integers, both coprime to 3, the congruence x 3 ≡ p (mod q) is solvable if and only if ...
(the Fibonacci sequence) is formed by starting with 0 and 1 and then adding any two consecutive terms to obtain the next one: an implicit description (sequence A000045 in the OEIS). The sequence 0, 3, 8, 15, ... is formed according to the formula n 2 − 1 for the nth term: an explicit definition.
The track is 100 meters long. Achilles could run at 10 m/s, while the tortoise only 5. The tortoise, with a 10-meter advantage, Zeno argued, would win. Achilles would have to move 10 meters to catch up to the tortoise, but the tortoise would already have moved another five meters by then.