On some properties of the series ∑k=0 kx and the Stirling numbers of the second kind |
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Authors: | Tam s Lengyel |
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Affiliation: | Mathematics Department, Occidental College, 1600 Campus Road, Los Angeles, CA 90041, USA |
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Abstract: | We partially characterize the rational numbers x and integers n 0 for which the sum ∑k=0∞ knxk assumes integers. We prove that if ∑k=0∞ knxk is an integer for x = 1 − a/b with a, b> 0 integers and gcd(a,b) = 1, then a = 1 or 2. Partial results and conjectures are given which indicate for which b and n it is an integer if a = 2. The proof is based on lower bounds on the multiplicities of factors of the Stirling number of the second kind, S(n,k). More specifically, we obtain for all integers k, 2 k n, and a 3, provided a is odd or divisible by 4, where va(m) denotes the exponent of the highest power of a which divides m, for m and a> 1 integers. New identities are also derived for the Stirling numbers, e.g., we show that ∑k=02nk! S(2n, k) , for all integers n 1. |
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