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A065108 Numbers expressible as a product of Fibonacci numbers. 8
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 13, 15, 16, 18, 20, 21, 24, 25, 26, 27, 30, 32, 34, 36, 39, 40, 42, 45, 48, 50, 52, 54, 55, 60, 63, 64, 65, 68, 72, 75, 78, 80, 81, 84, 89, 90, 96, 100, 102, 104, 105, 108, 110, 117, 120, 125, 126, 128, 130, 135, 136, 144, 150, 156, 160, 162 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

There are infinitely many triples of consecutive terms of this sequence that are consecutive integers, see A065885. John W. Layman, Nov 27 2001

Carmichael's theorem implies that 8 and 144 are the only Fibonacci numbers that are products of other Fibonacci numbers, cf. A235383. - Robert C. Lyons, Jan 13 2013

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

FORMULA

As Charles R Greathouse IV recently remarked, it would be good to have an asymptotic formula for this sequence. - N. J. A. Sloane, Jul 22 2012

EXAMPLE

52 = 2 * 2 * 13 is the product of Fibonacci numbers 2, 2 and 13.

MAPLE

with(combinat): A000045:=proc(n) options remember: RETURN(fibonacci(n)): end: mulfib:=proc(m, i) local j, q, f: f:=0: for j from i by -1 to 3 while(f=0) do if(irem(m, A000045(j))=0) then q:=iquo(m, A000045(j)): if(q=1) then RETURN(1) else f:=mulfib(q, j) fi fi od: RETURN(f): end: for i from 3 to 12 do for n from A000045(i) to A000045(i+1)-1 do m:=mulfib(n, i): if m=1 then printf("%d, ", n) fi od od: (C. Ronaldo)

MATHEMATICA

nn = 1000; k = 1; fib = {}; While[k++; f = Fibonacci[k]; f <= nn, AppendTo[fib, f]]; s = fib; While[s2 = Select[Union[s, Flatten[Outer[Times, fib, s]]], # <= nn &]; Length[s2] > Length[s], s = s2]; s (* T. D. Noe, Jul 17 2012 *)

CROSSREFS

Cf. A000045, A065885. Complement of A065105.

Cf. A049997 and A094563: F(i)*F(j) and (F(i)*F(j)*F(k) respectively.

Subsequence of A178772.

Sequence in context: A194467 A225857 A168134 * A094563 A228897 A068095

Adjacent sequences:  A065105 A065106 A065107 * A065109 A065110 A065111

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Nov 21 2001

EXTENSIONS

More terms from John W. Layman, Nov 27 2001

More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 02 2005

STATUS

approved

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Last modified April 25 00:50 EDT 2014. Contains 240991 sequences.