A121708 - OEIS

A121708

Numerator of Sum/Product of first n Fibonacci numbers A000045[n].

1, 2, 2, 7, 2, 1, 11, 3, 11, 1, 29, 47, 29, 1, 19, 41, 19, 1, 199, 23, 199, 1, 521, 281, 521, 1, 31, 2207, 31, 1, 3571, 107, 3571, 1, 9349, 2161, 9349, 1, 211, 13201, 211, 1, 64079, 1103, 64079, 1, 15251, 90481, 15251, 1, 5779, 14503, 5779, 1, 1149851, 2521

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OFFSET

1,2

COMMENTS

a(1) = 1 and a(4k+2) = 1 for k>0.

For k >1 a(4k-1) = a(4k+1) = A072183(2k+1) = A061447(2k+1) Primitive part of Lucas(n).

LINKS

Table of n, a(n) for n=1..56.

FORMULA

a(n) = numerator( sum(k=1..n, Fibonacci(k)) / prod(k=1..n, Fibonacci(k)) ).

MATHEMATICA

Table[Numerator[Sum[Fibonacci[k], {k, 1, n}]/Product[Fibonacci[k], {k, 1, n}]], {n, 1, 100}]

With[{fibs=Fibonacci[Range[60]]}, Numerator[Accumulate[fibs]/Rest[ FoldList[ Times, 1, fibs]]]] (* This is significantly faster than the first program above *) (* Harvey P. Dale, Aug 19 2012 *)

CROSSREFS

Cf. A000045, A000032, A079451, A001578, A096362, A058036, A121709, A090585.

Cf. A061447, A072183.

Sequence in context: A340180 A063706 A110779 * A286370 A138069 A208475

Adjacent sequences: A121705 A121706 A121707 * A121709 A121710 A121711

KEYWORD

frac,nonn

AUTHOR

Alexander Adamchuk, Aug 16 2006, Sep 21 2006

STATUS

approved