# A013140 (b-file synthesized from sequence entry) 0 1 1 2 2 4 3 4 4 -16 5 -88 6 64 7 2496 8 4096 9 -106624 10 -480896 11 6875136 12 54717440 13 -673392640 14 -7775895552 15 99550288896 16 1454255472640 17 -21279326830592 18 -360442602684416 19 6159283224084480 20 116460747215831040