# A018249 (b-file synthesized from sequence entry) 0 1 1 2 2 6 3 18 4 52 5 130 6 310 7 718 8 1618 9 3670 10 8160 11 17862 12 38872 13 84016 14 180502 15 386092 16 821640 17 1742536 18 3681130 19 7754076 20 16290046 21 34136028 22 71378568 23 148948138 24 310248240 25 645155196 26 1339484196 27 2777105128 28 5750079046