Mathematics – Number Theory
Scientific paper
2011-05-11
J. Integer Seq. 14 (2011) Article 11.6.2
Mathematics
Number Theory
11 pages, 3 tables. Corrected mistakes in the published version of Table 1, added corresponding Acknowledgment
Scientific paper
The $n$th Ramanujan prime is the smallest positive integer $R_n$ such that if $x \ge R_n$, then the interval $(x/2,x]$ contains at least $n$ primes. We sharpen Laishram's theorem that $R_n < p_{3n}$ by proving that the maximum of $R_n/p_{3n}$ is $R_5/p_{15} = 41/47$. We give statistics on the length of the longest run of Ramanujan primes among all primes $p<10^n$, for $n\le9$. We prove that if an upper twin prime is Ramanujan, then so is the lower; a table gives the number of twin primes below $10^n$ of three types. Finally, we relate runs of Ramanujan primes to prime gaps. Along the way we state several conjectures and open problems. The Appendix explains Noe's fast algorithm for computing $R_1,R_2,...,R_n$.
Nicholson John W.
Noe Tony D.
Sondow Jonathan
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