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An asymptotic approximation of Wallis’ sequence

Vito Lampret (2012)

Open Mathematics

An asymptotic approximation of Wallis’ sequence W(n) = Πk=1n 4k 2/(4k 2 − 1) obtained on the base of Stirling’s factorial formula is presented. As a consequence, several accurate new estimates of Wallis’ ratios w(n) = Πk=1n(2k−1)/(2k) are given. Also, an asymptotic approximation of π in terms of Wallis’ sequence W(n) is obtained, together with several double inequalities such as, for example, W ( n ) · ( a n + b n ) < π < W ( n ) · ( a n + b n ' ) with a n = 2 + 1 2 n + 1 + 2 3 ( 2 n + 1 ) 2 - 1 3 n ( 2 n + 1 ) ' b n = 2 33 ( n + 1 ) 2 ' b n ' 1 13 n 2 ' n .

An asymptotic expansion.

Mincu, Gabriel (2003)

JIPAM. Journal of Inequalities in Pure &amp; Applied Mathematics [electronic only]

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