OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..239 (terms below 10^10)
P. Hagis, Jr. and G. L. Cohen, Infinitary harmonic numbers, Bull. Australian math. Soc., 41 (1990), 151-158 (Math. Rev. 91d:11001) (asymptotics).
Eric Weisstein's World of Mathematics, Harmonic Mean
Wikipedia, Harmonic mean
MATHEMATICA
bitty[ k_ ] := Union[ Flatten[ Outer[ Plus, Sequence @@ ({0, #} & /@ Union[ (2^Range[ 0, Floor[ Log[ 2, k ] ] ] ) Reverse[ IntegerDigits[ k, 2 ] ] ] ) ] ] ]; 1 + Flatten[ Position[ Table[ (Length[ # ] /(Plus @@ (1/#)) &)@ (Apply[ Times, (First[ it ] ^ (# /. z -> List)) ] & /@ Flatten[ Outer[ z, Sequence @@ (bitty /@ Last[ it = Transpose[ FactorInteger[ k ] ] ] ), 1 ] ]), {k, 2, 2^22 + 1} ], _Integer ] ] (* Robert G. Wilson v, Sep 04 2001 *)
PROG
(Haskell)
import Data.Ratio (denominator)
import Data.List (genericLength)
a063947 n = a063947_list !! (n-1)
a063947_list = filter ((== 1) . denominator . hm . a077609_row) [1..]
where hm xs = genericLength xs / sum (map (recip . fromIntegral) xs)
-- Reinhard Zumkeller, Jul 10 2013
CROSSREFS
KEYWORD
nonn,nice,changed
AUTHOR
Wouter Meeussen, Sep 03 2001
EXTENSIONS
More terms from David W. Wilson, Sep 04 2001
STATUS
approved