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A001901
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Successive numerators of Wallis's approximation to pi/2 (reduced).
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3
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1, 2, 4, 16, 64, 128, 256, 2048, 16384, 32768, 65536, 262144, 1048576, 2097152, 4194304, 67108864, 1073741824, 2147483648, 4294967296, 17179869184, 68719476736, 137438953472, 274877906944, 2199023255552
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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REFERENCES
| H.-D. Ebbinghaus et al., Numbers, Springer, 1990, p. 146.
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LINKS
| J. Sondow, A faster product for Pi and a new integral for ln(Pi/2), Amer. Math. Monthly 112 (2005), 729-734 and 113 (2006), 670.
Eric Weisstein's World of Mathematics, Pi
Eric Weisstein's World of Mathematics, Pi Continued Fraction
Index to divisibility sequences
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FORMULA
| ... 2.2.4.4.6.6....2n.2n/1.3.3.5.5.7.7....(2n-1).(2n+1) ...
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CROSSREFS
| Denominators are A001902. Subsequence of A000079.
Sequence in context: A138867 A138868 A138871 * A127588 A092585 A106186
Adjacent sequences: A001898 A001899 A001900 * A001902 A001903 A001904
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KEYWORD
| nonn,frac
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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