A121171 Largest prime divisor of Lucas(5*n), where Lucas(k) = A000032(k).

11, 41, 31, 2161, 151, 2521, 911, 3041, 541, 570601, 39161, 20641, 24571, 12317523121, 18451, 23725145626561, 12760031, 10783342081, 87382901, 5738108801, 767131, 59996854928656801, 686551, 23735900452321, 28143378001, 42426476041450801, 119611

Offset: 1

Author

Alexander Adamchuk, Aug 14 2006

Keywords

• nonn

Comments

Final digit of a(n) is 1. Mod[a(n),10] = 1. Final digit of many prime divisors of Lucas(5*n) is 1.

Links

• Daniel Suteu, Table of n, a(n) for n = 1..309

Crossrefs

Cf. A000032, A000045, A079451.

Programs

Mathematica

Table[Max[Flatten[FactorInteger[Fibonacci[5n-1]+Fibonacci[5n+1]]]],{n,1,40}]

PARI

lucas(n) = fibonacci(n+1)+fibonacci(n-1); \\ A000032
a(n) = vecmax(factor(lucas(5*n))[,1]); \\ Daniel Suteu, May 26 2022

Formula

a(n) = A006530(A000032(5*n)) = A079451(5*n). - Daniel Suteu, May 26 2022