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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. The Pell numbers have P n = 2P n−1 + P n−2.
Some real numbers have decimal expansions that eventually get into loops, endlessly repeating a sequence of one or more digits: 1 ⁄ 3 = 0.33333... 1 ⁄ 7 = 0.142857142857... 1318 ⁄ 185 = 7.1243243243... Every time this happens the number is still a rational number (i.e. can alternatively be represented as a ratio of an integer and a ...
As of September 2015, the largest confirmed Lucas prime is L 148091, which has 30950 decimal digits. As of August 2022, the largest known Lucas probable prime is L 5466311, with 1,142,392 decimal digits. If L n is prime then n is 0, prime, or a power of 2. L 2 m is prime for m = 1, 2, 3, and 4 and no other known values of m.
For example, in the decimal system (base 10), the numeral 4327 means (4×10 3) + (3×10 2) + (2×10 1) + (7×10 0), noting that 10 0 = 1. In general, if b is the base, one writes a number in the numeral system of base b by expressing it in the form a n b n + a n − 1 b n − 1 + a n − 2 b n − 2 + ... + a 0 b 0 and writing the enumerated ...
An odd number does not have the prime factor 2. The first: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23 (sequence A005408 in the OEIS). All integers are either even or odd. A square has even multiplicity for all prime factors (it is of the form a 2 for some a). The first: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144 (sequence A000290 in the OEIS).
A list of articles about numbers (not about numerals). Topics include powers of ten, notable integers, prime and cardinal numbers, and the myriad system.
The set of rational numbers is not complete. For example, the sequence (1; 1.4; 1.41; 1.414; 1.4142; 1.41421; ...), where each term adds a digit of the decimal expansion of the positive square root of 2, is Cauchy but it does not converge to a rational number (in the real numbers, in contrast, it converges to the positive square root of 2).
Also called primes congruent to d modulo a . The primes of the form 2 n +1 are the odd primes, including all primes other than 2. Some sequences have alternate names: 4 n +1 are Pythagorean primes, 4 n +3 are the integer Gaussian primes, and 6 n +5 are the Eisenstein primes (with 2 omitted).