RosettaCodeData/Task/Van-Eck-sequence/Sidef/van-eck-sequence.sidef

func van_eck(n) {

    var seen = Hash()
    var seq  = [0]
    var prev = seq[-1]

    for k in (1 ..^ n) {
        seq << (seen.has(prev) ? (k - seen{prev}) : 0)
        seen{prev} = k
        prev = seq[-1]
    }

    seq
}

say van_eck(10)
say van_eck(1000).last(10)