numlib::prevprime -- next
smaller prime
IntroductionFor an integer a
numlib::prevprime(a) returns the greatest
prime number . If a then
numlib::prevprime(a) returns
FAIL.
Call(s)numlib::prevprime(a)
numlib::prevprime(symb)
Parametersa |
- | an integer |
Returnsnumlib::prevprime(a) returns either a
natural number or FAIL.
Related
Functionsisprime, ithprime, nextprime, numlib::proveprime
Detailsnumlib::prevprime returns the function call with
evaluated argument if the argument is not a number.numlib::prevprime returns an error if the argument
evaluates to a number which is not an integer.
Example
1Computing the largest prime <=15485865:
>> numlib::prevprime(15485865)
15485863
Example
2There are no primes :
>> numlib::prevprime(1)
FAIL
Backgroundnumlib::prevprime uses isprime.