OFFSET
1,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..2000 (first 300 terms from Paolo P. Lava)
FORMULA
From definition a(n) = Sum_{d|n} F(d)*phi(n/d); also a(n) = Sum_{k=1..n} gcd(F(k), F(k+n)) where F(k) denotes the k-th Fibonacci number. - Benoit Cloitre, May 25 2003
G.f.: Sum_{k>=1} phi(k) * x^k/(1 - x^k - x^(2*k)). - Ilya Gutkovskiy, Jul 23 2019
a(n) ~ phi^n / sqrt(5), where phi = A001622 = (1+sqrt(5))/2 is the golden ratio. - Vaclav Kotesovec, Jul 23 2019
From Richard L. Ollerton, May 06 2021: (Start)
a(n) = Sum_{k=1..n} F(gcd(n,k)).
a(n) = Sum_{k=1..n} F(n/gcd(n,k))*phi(gcd(n,k))/phi(n/gcd(n,k)). (End)
MATHEMATICA
Table[Sum[Fibonacci[d] EulerPhi[n/d], {d, Divisors[n]}], {n, 1, 50}] (* Vincenzo Librandi, Aug 19 2018 *)
PROG
(PARI) a(n)=sumdiv(n, d, fibonacci(d)*eulerphi(n/d))
(Magma) [&+[Fibonacci(d)*EulerPhi(n div d): d in Divisors(n)]: n in [1..50]]; // Vincenzo Librandi, Aug 19 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved