Primes and ... 'not-primes'

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{--

Primes, and ... 'not primes'

Question: what is the opposite of 'prime,' as in 'prime numbers'?

'Plain' numbers?

'Secondary' numbers?

Anyway.

I read on the internet, so it must be true, that for every
prime number, p, there follows sometime after it a run
of at least p-consecutive numbers that are not prime.

So: 2 has [8, 9]
    3 has [8, 9, 10]
    5 has [720, 721, 722, 723, 724]
    ...

That last one was a big hint (and there is always the 'internets').

Write a function: --}

plainRun :: Integer -> [Integer]
plainRun prime = undefined

{-- such that for a prime number, prime, it returns a list
of not-prime consecutive numbers of length prime.

This exercise was inspired by the tweet from @AlgebraFact:

"For every n, you can find a span of n consecutive numbers 
containing no primes."

tweeted on July 8th, 2014 --}