Ramanujan prime
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Ramanujan primes are the integers Rn that are the smallest to satisfy the condition pi(x) - pi(x/2) > n, for all x > Rn. In other words, there are at least n primes between x/2 and x, whenever x is greater than or equal to Rn. The sequence begins 2, 11, 17, 29, 41, ....

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