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- #!/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]); \\ ~~~~
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