primepi([from,until])

["Ruud H.G. van Tol" <rvtol@isolution.nl>]

I'm adding

a(n) = #primes([n^2/4, (n+1)^2/4]);

to https://oeis.org/A220492

and was wondering if primepi() should grow a primepi([x1, x2])variant,
to return the number of primes p, x1 <= p <= x2.

-- Ruud

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