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There is a newer version: 3.2.1

#
# https://fr.wikipedia.org/wiki/Pi#Suites_r.C3.A9cursives
#
prefix ex: 
select (ex:pi(?n) as ?pi) ?n
where {


function ex:a(?n) { 
 if (?n = 0, 1, (ex:a(?n - 1) + ex:b(?n - 1)) / 2)
}

function ex:b (?n) {
  if (?n = 0, power(1/2, 1/2),
    power(ex:a(?n - 1) * ex:b(?n - 1), 1/2))
}

function ex:c(?n) {
  if (?n = 0, 1/4,
    ex:c(?n - 1) - power(2, ?n - 1) * 
      power((ex:a(?n - 1) - ex:b(?n - 1)) / 2, 2))
}

function ex:pi(?n) {
  (power(ex:a(?n) + ex:b(?n), 2) / (4 * ex:c(?n)))
}



bind (unnest(xt:iota(5)) as ?n)

}
order by desc(?n)