prog.sf

#!/usr/bin/ruby

# Largest prime factor of central factorial number A001819[n].
# https://oeis.org/A120298

# a(n) = A006530(A001819(n)). - ~~~~

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

func a(n) {
    (n!)**2 * sum(1..n, {|k| 1/k.sqr })
    #numerator( sum(1..n, {|k| 1/k.sqr }))
}

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

for n in (2..10000) {
    var k = a(n)
    var row = "#{n} #{gpf(k)||1}"
    say row
    bfile.say(row)
}

__END__

# PARI/GP script

a(n) = vecmax(factor(n!^2 * sum(k=1, n, 1/k^2))[,1]); \\ ~~~~