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Register a new userOn binomial coefficients associated with Sierpi{n}ski and Riesel numbers
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In this paper, we investigate the existence of Sierpi{n}ski numbers and Riesel numbers as binomial coefficients. We show that for any odd positive integer $r$, there exist infinitely many Sierpi{n}ski numbers and Riesel numbers of the form $binom{k}{r}$. Let $S(x)$ be the number of positive integers $r$ satisfying $1leq rleq x$ for which $binom{k}{r}$ is a Sierpi{n}ski number for infinitely many $k$. We further show that the value $S(x)/x$ gets arbitrarily close to 1 as $x$ tends to infinity. Generalizations to base $a$-Sierpi{n}ski numbers and base $a$-Riesel numbers are also considered. In particular, we prove that there exist infinitely many positive integers $r$ such that $binom{k}{r}$ is simultaneously a base $a$-Sierpi{n}ski and base $a$-Riesel number for infinitely many $k$.
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