primefactors(n): an iterator on the primes that evenly divide n (repeating such as the product is n

(I don't have a good name): something telling that an integer can be represented exactly as a float

On 12 July 2018 at 12:55, Serhiy Storchaka storchaka@gmail.com wrote:

What are your thoughts about adding a new imath module for integer mathematics? It could contain the following functions:

- factorial(n)
Is just moved from the math module, but non-integer types are rejected. Currently math.factorial() accepts also integer floats like 3.0. It looks to me, the rationale was that at the time when math.factorial() was added, all function in the math module worked with floats. But now we can revise this decision.

- gcd(n, m)
Is just moved from the math module.

- as_integer_ration(x)
Equivalents to:

def as_integer_ration(x): if hasattr(x, 'as_integer_ration'): return x.as_integer_ration() else: return (x.numerator, x.denominator)

- binom(n, k)
Returns factorial(n) // (factorial(k) * factorial(n-k)), but uses more efficient algorithm.

- sqrt(n)
Returns the largest integer r such that r**2 <= n and (r+1)**2 > n.

- isprime(n)
Tests if n is a prime number.

- primes()
Returns an iterator of prime numbers: 2, 3, 5, 7, 11, 13,...

Are there more ideas?

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