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A053988
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Denominators of successive convergents to tan(1/2) using continued fraction 1/(2-1/(6-1/(10-1/(14-1/(18-1/(22-1/(26-1/30-...))))))).
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1
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2, 11, 108, 1501, 26910, 590519, 15326584, 459207001, 15597711450, 592253828099, 24859063068708, 1142924647332469, 57121373303554742, 3083411233744623599, 178780730183884614000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n)=sum(k=0, floor(n/2), (-1)^k*(2*n-2*k)!/(n-2*k)!/(2*k)!) - Benoit Cloitre (benoit7848c(AT)orange.fr), Jan 03 2006
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PROG
| (PARI) a(n)=sum(k=0, floor(n/2), (-1)^k*(2*n-2*k)!/(n-2*k)!/(2*k)!) (Cloitre)
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CROSSREFS
| Cf. A053987.
Sequence in context: A118805 A198001 A207155 * A141314 A099933 A098437
Adjacent sequences: A053985 A053986 A053987 * A053989 A053990 A053991
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KEYWORD
| easy,frac,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Apr 03 2000
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