login
Denominator of Sum_{k=1..n} 1/L(k) where L(n) is the n-th Lucas number (A000204).
2

%I #8 Mar 11 2015 11:23:09

%S 1,3,12,84,924,2772,80388,3778236,35893242,1471622922,292852961478,

%T 3367809056997,1754628518695437,493050613753417797,

%U 61138276105423806828,134932175364670341669396,481842798227237790101413116,154671538230943330622553610236

%N Denominator of Sum_{k=1..n} 1/L(k) where L(n) is the n-th Lucas number (A000204).

%e 1, 4/3, 19/12, 145/84, 1679/924, 5191/2772, ... = A225904/A225905.

%t Denominator[Table[Sum[1/LucasL[k], {k, 1, n}], {n, 1, 30}]]

%t Denominator[Accumulate[1/LucasL[Range[20]]]] (* _Harvey P. Dale_, Mar 11 2015 *)

%Y Cf. A000204, A059248, A035105, A225904.

%K nonn,frac,easy

%O 1,2

%A _Michel Lagneau_, May 20 2013