A225905 Denominator of Sum_{k=1..n} 1/L(k) where L(n) is the n-th Lucas number (A000204).
1, 3, 12, 84, 924, 2772, 80388, 3778236, 35893242, 1471622922, 292852961478, 3367809056997, 1754628518695437, 493050613753417797, 61138276105423806828, 134932175364670341669396, 481842798227237790101413116, 154671538230943330622553610236
Offset: 1
Examples
1, 4/3, 19/12, 145/84, 1679/924, 5191/2772, ... = A225904/A225905.
Programs
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Mathematica
Denominator[Table[Sum[1/LucasL[k], {k, 1, n}], {n, 1, 30}]] Denominator[Accumulate[1/LucasL[Range[20]]]] (* Harvey P. Dale, Mar 11 2015 *)