oeis.orgA072171 - OEIS 2, 6, 14, 71, 190, 610, 1929, 5946, 17765, 51094, 140062, 409194, 1196690, 3481113, 10126390, 29457184, 85689537, 249266759, 725105060, 2109295881, 6135840666, 17848866544 (list; graph; refs; listen; history; text; internal format)