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Search: id:A103639
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| 1, 15, 945, 135135, 34459425, 13749310575, 7905853580625, 6190283353629375, 6332659870762850625, 8200794532637891559375, 13113070457687988603440625, 25373791335626257947657609375
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OFFSET
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0,2
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FORMULA
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(4n+2)! / [2 * 4^n * (2n+1)! ].
E.g.f.: sinh(x^2/2) = x^2/2! + 15x^6/6! + 945x^10/10! +...
Recurrence: a(n+1) = (4n-1)(4n+1)*a(n), a(0) = 1.
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EXAMPLE
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Sequence starts 1, 1*3*5, 1*3*5*7*9, 1*3*5*7*9*11*13, ...
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CROSSREFS
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Bisection of the double factorials A001147. Cf. A102992.
Cf. Odd part of A024343 and A009564.
Sequence in context: A157462 A042747 A136419 this_sequence A055413 A067408 A102102
Adjacent sequences: A103636 A103637 A103638 this_sequence A103640 A103641 A103642
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KEYWORD
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nonn
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AUTHOR
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Ralf Stephan (ralf(AT)ark.in-berlin.de), Feb 18 2005
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