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The fifteen different rooted binary trees (with unordered children) on a set of four labeled leaves, illustrating 15 = (2 × 4 − 3)‼ (see article text). Double factorials are motivated by the fact that they occur frequently in enumerative combinatorics and other settings. For instance, n‼ for odd values of n counts
As one special case, it can be used to prove that if n is a positive integer then 4 divides () if and only if n is not a power of 2. It follows from Legendre's formula that the p -adic exponential function has radius of convergence p − 1 / ( p − 1 ) {\displaystyle p^{-1/(p-1)}} .
This experiment is an example of a 2 2 (or 2×2) factorial experiment, so named because it considers two levels (the base) for each of two factors (the power or superscript), or #levels #factors, producing 2 2 =4 factorial points. Cube plot for factorial design . Designs can involve many independent variables.
2.4 Modified-factorial denominators. 2.5 Binomial coefficients. 2.6 Harmonic numbers. 3 Binomial coefficients. 4 Trigonometric functions. 5 Rational functions.
That is, given k factors, the k th column consists of 2 (k - 1) minus signs (i.e., the low level of the factor) followed by 2 (k - 1) plus signs (i.e., the high level of the factor). For example, for a full factorial design with three factors, the design matrix is
In this article, the symbol () is used to represent the falling factorial, and the symbol () is used for the rising factorial. These conventions are used in combinatorics , [ 4 ] although Knuth 's underline and overline notations x n _ {\displaystyle x^{\underline {n}}} and x n ¯ {\displaystyle x^{\overline {n}}} are increasingly popular.
English: The table of signs for a 3-factor, 2-level factorial design used to calculate the effect estimates for each treatment combination. Date: 30 November 2017:
Use divide and conquer to compute the product of the primes whose exponents are odd; Divide all of the exponents by two (rounding down to an integer), recursively compute the product of the prime powers with these smaller exponents, and square the result; Multiply together the results of the two previous steps