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This "Rule of 70" gives accurate doubling times to within 10% for growth rates less than 25% and within 20% for rates less than 60%. Larger growth rates result in the rule underestimating the doubling time by a larger margin. Some doubling times calculated with this formula are shown in this table. Simple doubling time formula:
In mathematics, a product is the result of multiplication, or an expression that identifies objects (numbers or variables) to be multiplied, called factors.For example, 21 is the product of 3 and 7 (the result of multiplication), and (+) is the product of and (+) (indicating that the two factors should be multiplied together).
m is a divisor of n (also called m divides n, or n is divisible by m) if all prime factors of m have at least the same multiplicity in n. The divisors of n are all products of some or all prime factors of n (including the empty product 1 of no prime factors). The number of divisors can be computed by increasing all multiplicities by 1 and then ...
Factors p 0 = 1 may be inserted without changing the value of n (for example, 1000 = 2 3 ×3 0 ×5 3). In fact, any positive integer can be uniquely represented as an infinite product taken over all the positive prime numbers, as
For example, to find the prime factors of n = 70, one can try to divide 70 by successive primes: first, 70 / 2 = 35; next, neither 2 nor 3 evenly divides 35; finally, 35 / 5 = 7, and 7 is itself prime. So 70 = 2 × 5 × 7. Trial division was first described by Fibonacci in his book Liber Abaci (1202). [1]
Continuing this process until every factor is prime is called prime factorization; the result is always unique up to the order of the factors by the prime factorization theorem. To factorize a small integer n using mental or pen-and-paper arithmetic, the simplest method is trial division : checking if the number is divisible by prime numbers 2 ...
Applying Legendre's formula to the product formula for binomial coefficients produces Kummer's theorem, a similar result on the exponent of each prime in the factorization of a binomial coefficient. [55] Grouping the prime factors of the factorial into prime powers in different ways produces the multiplicative partitions of factorials. [56]
When such a divisor is found, the repeated application of this algorithm to the factors q and n / q gives eventually the complete factorization of n. [1] For finding a divisor q of n, if any, it suffices to test all values of q such that 1 < q and q 2 ≤ n. In fact, if r is a divisor of n such that r 2 > n, then q = n / r is a divisor of n ...