recamanSucc: function [seen, n, r].memoize[
    back: r - n
    (or? 0 > back contains? seen back)? -> n + r
                                        -> back
]

recamanUntil: function [p][
    n: 1
    r: 0
    rs: @[r]
    seen: rs
    blnNew: true
    while [not? do p][
        r: recamanSucc seen n r
        blnNew: not? in? r seen
        seen: unique seen ++ r
        'rs ++ r
        inc 'n
    ]
    return rs
]

print "First 15 Recaman numbers:"
print recamanUntil [n = 15]

print ""
print "First duplicate Recaman number:"
print last recamanUntil [not? blnNew]