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A025550 a(n) = ( 1/1 + 1/3 + 1/5 + ... + 1/(2*n-1) )*LCM(1, 3, 5, ..., 2*n-1). 9
1, 4, 23, 176, 563, 6508, 88069, 91072, 1593269, 31037876, 31730711, 744355888, 3788707301, 11552032628, 340028535787, 10686452707072, 10823198495797, 10952130239452, 409741429887649, 414022624965424, 17141894231615609 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Or, numerator of 1/1 + 1/3 + ... + 1/(2n-1) up to a(38).

Following similar remark by T. D. Noe in A025547, this coincides with f(n) = numerator of 1+1/3+1/5+1/7+...+1/(2n-1) iff n <= 38. But a(39) = 18048708369314455836683437302413, f(39)=1640791669937677803334857936583. Note that f(n)=numerator(digamma(n+1/2)/2+log(2)+euler_gamma/2). - Paul Barry, Aug 19 2005

LINKS

Jean-François Alcover, Table of n, a(n) for n = 1..200

Eric Weisstein's World of Mathematics, Jeep Problem

MAPLE

a:= n-> (f-> add(1/p, p=f)*ilcm(f[]))([2*i-1$i=1..n]):

seq(a(n), n=1..40);  # Alois P. Heinz, Apr 16 2015

MATHEMATICA

With[{odds=Range[1, 71, 2]}, Table[Total[1/Take[odds, n]]LCM@@Take[odds, n], {n, 30}]] (* Harvey P. Dale, Aug 21 2011 *)

(* Only up to a(38) *) Numerator[Accumulate[1/Range[1, 2*38-1, 2]]] (* Harvey P. Dale, Mar 30 2015, updated by Jean-François Alcover, Apr 16 2015 *)

PROG

(Haskell)

a025550 n = numerator $ sum  $ map (1 %) $ take n [1, 3 ..]

-- Reinhard Zumkeller, Jan 22 2012

(PARI) a(n)=my(v=vector(n, i, 2*i-1)); sum(i=1, #v, 1/v[i])*lcm(v) \\ Charles R Greathouse IV, Feb 28 2013

(MAGMA) [&+[1/d: d in i]*Lcm(i) where i is [1..2*n-1 by 2]: n in [1..21]]; // Bruno Berselli, Apr 16 2015

CROSSREFS

Cf. A025547, A075135, A002428.

Sequence in context: A127131 A083355 A141763 * A067545 A004041 A220353

Adjacent sequences:  A025547 A025548 A025549 * A025551 A025552 A025553

KEYWORD

nonn,easy,nice,frac

AUTHOR

Clark Kimberling

EXTENSIONS

Value of a(39) corrected by Jean-François Alcover, Apr 16 2015

STATUS

approved

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Last modified September 21 23:55 EDT 2019. Contains 327286 sequences. (Running on oeis4.)