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 A065108 Positive numbers expressible as a product of Fibonacci numbers. 12
 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 Clemens Heuberger and Stephan Wagner, On the monoid generated by a Lucas sequence, arXiv:1606.02639 [math.NT], 2016. 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 *) PROG (PARI) list(lim)=if(lim<7, return([1..lim\1])); my(v=List([1]), F=List([2, 3]), curfib, t, idx, newidx); while((t=F[#F]+F[#F-1])<=lim, listput(F, t)); F=setminus(Set(F), [8, 144]); for(i=1, #F, curfib=F[i]; idx=1; while(v[idx]*curfib<=lim, newidx=#v+1; for(j=idx, #v, t=curfib*v[j]; if(t<=lim, listput(v, t))); idx=newidx)); Set(v) \\ Charles R Greathouse IV, Jun 15 2017 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: A168134 A245030 A245027 * A094563 A228897 A068095 Adjacent sequences:  A065105 A065106 A065107 * A065109 A065110 A065111 KEYWORD nonn,changed 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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