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A012393
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arctanh(tan(x)*tan(x))=2/2!*x^2+16/4!*x^4+512/6!*x^6+34816/8!*x^8...
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3
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2, 16, 512, 34816, 4063232, 724566016, 183240753152, 62382319599616, 27507470234550272, 15250953398036463616, 10384044045105304174592, 8517992937742473694806016, 8285310016381680852100186112
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| a(n) = A000828(2n+1).
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FORMULA
| E.g.f.: ln(sec(2*x))/2, cf. A000182. - Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 04 2005
a(n) = (-1)^(n(2n+1))4^(2n+1)(E{2n+1}(1/2)+E{2n+1}(1)); E_{n}(x) Euler polynomial. [Peter Luschny, Nov 25 2010]
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MAPLE
| A012393 := n -> (-1)^(n*(2*n+1))*4^(2*n+1)*(euler(2*n+1, 1/2) + euler(2*n+1, 1)) end; [Peter Luschny, Nov 25 2010]
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CROSSREFS
| Sequence in context: A140311 A012389 A009710 * A189899 A189335 A189773
Adjacent sequences: A012390 A012391 A012392 * A012394 A012395 A012396
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KEYWORD
| nonn
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AUTHOR
| Patrick Demichel (dml(AT)hpfrcu03.france.hp.com)
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