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numlib::prevprime -- next smaller prime

Introduction

For 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)

Parameters

a - an integer

Returns

numlib::prevprime(a) returns either a natural number or FAIL.

Related Functions

isprime, ithprime, nextprime, numlib::proveprime

Details

Example 1

Computing the largest prime <=15485865:

>> numlib::prevprime(15485865)
                                 15485863

Example 2

There are no primes :

>> numlib::prevprime(1)
                                   FAIL

Background

Changes




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