prog.sf

#!/usr/bin/ruby

# Largest prime divisor of Lucas[5n], where Lucas[k] = A000032[k].
# https://oeis.org/A121171

# First several terms of the sequence:
#   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

# a(n) = A006530(A000032(5*n)) = A079451(5*n). - ~~~~

include("../../../factordb/auto.sf")

func a(n) {
    lucas(5*n)
}

var bfile = File("bfile.txt").open_w.autoflush(true)

for n in (1..10000) {
    var k = a(n)
    var row = "#{n} #{gpf(k)||1}"
    say row
    bfile.say(row)
}

__END__

# PARI/GP script

lucas(n) = fibonacci(n+1)+fibonacci(n-1); \\ A000032
a(n) = vecmax(factor(lucas(5*n))[,1]); \\ ~~~~