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A061446 Primitive part of Fibonacci(n). 28
1, 1, 2, 3, 5, 4, 13, 7, 17, 11, 89, 6, 233, 29, 61, 47, 1597, 19, 4181, 41, 421, 199, 28657, 46, 15005, 521, 5777, 281, 514229, 31, 1346269, 2207, 19801, 3571, 141961, 321, 24157817, 9349, 135721, 2161, 165580141, 211, 433494437, 13201, 109441 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Fib(n) = A000045(n) = Product_{d|n} a(d), Lucas(n) = A000204(n) = Product_{d|2n and 2^m|d iff 2^m|2n} a(d) (e.g., Lucas(4) = 7 = a(8), Lucas(6) = 18 = a(12)*a(4)). - Len Smiley, Nov 11 2001
A 2001 Iranian Mathematical Olympiad question shows such a sequence exists whenever gcd(a(m),a(n)) = a(gcd(m,n)).
The problem of the characterization of the family of all GCD-morphic sequences F, i.e., F such that GCD(F(m),F(n)) = F(GCD(m,n)), was posed by A. K. Kwasniewski (GCD-morphic Problem). Dziemianczuk and Bajguz (2008) showed that any GCD-morphic sequence is coded by a certain natural number-valued sequence. - Maciej Dziemianczuk, Jan 15 2009
This is the LCM-transform of the Fibonacci numbers (cf. Nowicki). - N. J. A. Sloane, Jan 02 2016
LINKS
N. Bliss, B. Fulan, S. Lovett, and J. Sommars, Strong Divisibility, Cyclotomic Polynomials, and Iterated Polynomials, Amer. Math. Monthly, 120 (2013), 519-536.
John Brillhart, Peter L. Montgomery and Robert D. Silverman, Tables of Fibonacci and Lucas factorizations, Math. Comp. 50 (1988), pp. 251-260, S1-S15. Math. Rev. 89h:11002.
R. D. Carmichael, On the numerical factors of the arithmetic forms alpha*n+-beta*n, Annals of Math., 2nd ser., 15 (1/4) (1913/14) 30-48.
M. Dziemianczuk and W. Bajguz, On GCD-morphic sequences, arXiv:0802.1303 [math.CO], 2008.
A. K. Kwasniewski, Cobweb posets as noncommutative prefabs, Adv. Stud. Contemp. Math. vol.14 (1) 2007. pp. 37-47.
Rohit Nagpal and A. Snowden, The module theory of divided power algebras, arXiv preprint arXiv:1606.03431 [math.AC], 2016.
A. Nowicki, Strong divisibility and LCM-sequences, arXiv:1310.2416 [math.NT], 2013.
A. Nowicki, Strong divisibility and LCM-sequences, Am. Math. Mnthly 122 (2015), 958-966.
FORMULA
Let r=(1+sqrt(5))/2. For n>2, the primitive part of F(n)=(r^n-(-1/r)^n)/sqrt(5) is Phi_n(-r^2)/r^phi(n) where Phi_n is n-th cyclotomic polynomial and phi is Euler's totient function A000010.
a(n) = Product_{d|n} Fib(d)^mu(n/d), where mu = A008683 (Bliss, Fulan, Lovett, Sommars, eq. (7)). - Jonathan Sondow, Jun 11 2013
a(n) = lcm(Fib(1),Fib(2),...,Fib(n))/lcm(Fib(1),Fib(2),...,Fib(n-1)). - Thomas Ordowski, Aug 03 2015
a(n) = Product_{k=1..n} Fib(gcd(n,k))^(mu(n/gcd(n,k))/phi(n/gcd(n,k))) = Product_{k=1..n} Fib(n/gcd(n,k))^(mu(gcd(n,k))/phi(n/gcd(n,k))) where mu = A008683, phi = A000010. - Richard L. Ollerton, Nov 08 2021
MAPLE
N:= 200; # to get a(1) to a(N)
L[0]:= 1:
for i from 1 to N do L[i]:=ilcm(L[i-1], combinat:-fibonacci(i)) od:
seq(L[i]/L[i-1], i=1..N); # Robert Israel, Aug 03 2015
MATHEMATICA
t={1}; Do[f=Fibonacci[n]; Do[f=f/GCD[f, t[[d]]], {d, Most[Divisors[n]]}]; AppendTo[t, f], {n, 2, 100}]; t
(* Second program: *)
a[n_] := Product[Fibonacci[d]^MoebiusMu[n/d], {d, Divisors[n]}];
Array[a, 45] (* Jean-François Alcover, Jul 04 2019 *)
PROG
(PARI) a(n)=my(d=divisors(n)); fibonacci(n)/lcm(apply(fibonacci, d[1..#d-1])) \\ Charles R Greathouse IV, Oct 06 2016
CROSSREFS
Cf. A000010 (comments on product formulas).
Sequence in context: A271862 A309373 A131401 * A280690 A240000 A193770
KEYWORD
nonn
AUTHOR
David Broadhurst, Jun 10 2001
EXTENSIONS
More terms from Vladeta Jovovic, Nov 09 2001
Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 29 2007
Edited by Charles R Greathouse IV, Oct 28 2009
STATUS
approved

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Last modified July 25 11:06 EDT 2024. Contains 374588 sequences. (Running on oeis4.)