Erratum (for erdosproblems.com/616, not the paper): the background's floorless paraphrase '3r/16 + 7/8 <= t(r) <= r/5' is internally inconsistent for every r < 70 (lower exceeds upper, e.g. 2.0 > 1.2 at r=6). The actual EHT91 statements — upper bound ceil(r/5) (Theorem 3, all r>=3) and lower bound floor(3r/16+7/8) (p.80) — are consistent for all r, and combined with their Theorem 6(II) they already pin t(r)=ceil(r/5) for all 3<=r<=20; the first value their results leave open is t(21) in {4,5}. Additionally, EHT91's own p.84 display '(3r-3,1) -\-> floor(3r/16+7/8)' is off by one against its own construction (tau = x+1 with x = floor(3r/16-1/8) witnesses -\-> of x, not x+1); p.80's phrasing is the intended claim.