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A072172
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(2*n+1)*5^(2*n+1).
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3
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5, 375, 15625, 546875, 17578125, 537109375, 15869140625, 457763671875, 12969970703125, 362396240234375, 10013580322265625, 274181365966796875, 7450580596923828125, 201165676116943359375, 5401670932769775390625, 144354999065399169921875
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| J. Machin (died 1751) used Pi/4 = 4*Sum_{n=0..inf} (-1)^n/((2*n+1)*5^(2*n+1)) - Sum_{n=0..inf} (-1)^n/((2*n+1)*239^(2*n+1)) to calculate Pi to 100 decimal places.
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REFERENCES
| H. Doerrie, 100 Great Problems of Elementary Mathematics, Dover, NY, 1965, p. 73
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CROSSREFS
| Cf. A072173.
Cf. A157332. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 03 2009]
Sequence in context: A121668 A160193 A098038 * A206386 A198902 A100474
Adjacent sequences: A072169 A072170 A072171 * A072173 A072174 A072175
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Jun 30 2002
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