A121170 Largest prime divisor of Fibonacci(5n).

5, 11, 61, 41, 3001, 61, 141961, 2161, 109441, 3001, 474541, 2521, 14736206161, 141961, 230686501, 3041, 3415914041, 109441, 67735001, 570601, 8288823481, 474541, 2441738887963981, 20641, 158414167964045700001, 14736206161, 1114769954367361, 12317523121, 349619996930737079890201

Offset

1,1

Comments

Except for a(1) = 5 all a(n) are congruent to 1 (mod 10) (final digit is 1). Final digit of most prime divisors of F(5n) is 1.

Links

Amiram Eldar, Table of n, a(n) for n = 1..284

Formula

a(n) = A060385(5*n).

Example

a(2) = 11 because F(10)= 5 * 11.
a(4) = 41 because F(20)= 3 * 5 * 11 * 41.
a(10) = 3001 because F(50)= 5^2 * 11 * 101 * 151 * 3001.
a(25) = 158414167964045700001 because F(125)= 5^3 * 3001 * 158414167964045700001.

Mathematica

Table[Max[Flatten[FactorInteger[Fibonacci[5n]]]], {n, 1, 50}]

Crossrefs

Cf. A000045, A060385.

Sequence in context: A095150 A215759 A041697 * A239322 A101209 A216071

Adjacent sequences: A121167 A121168 A121169 * A121171 A121172 A121173

Keyword

nonn

Author

Alexander Adamchuk, Aug 14 2006

Extensions

a(27)-a(29) from Amiram Eldar, Aug 01 2024

Status

approved