3v4l.org

run code in 150+ php & hhvm versions
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<?php $i = 1; for($f = 0; $f <= 20; $f++) { echo "F".$f." = ".abs((($f-1)+$f-2))."\n"; $i++; }
based on grInQ
Output for 4.3.0 - 7.1.0
F0 = 3 F1 = 1 F2 = 1 F3 = 3 F4 = 5 F5 = 7 F6 = 9 F7 = 11 F8 = 13 F9 = 15 F10 = 17 F11 = 19 F12 = 21 F13 = 23 F14 = 25 F15 = 27 F16 = 29 F17 = 31 F18 = 33 F19 = 35 F20 = 37