# A103931 (b-file synthesized from sequence entry) 1 1 2 4 3 36 4 144 5 3600 6 400 7 19600 8 78400 9 6350400 10 6350400 11 768398400 12 768398400 13 129859329600 14 129859329600 15 129859329600 16 519437318400 17 150117385017600 18 16679709446400 19 6021375110150400 20 240855004406016 21 26761667156224