A178845 Number of permutations of 2..n+1 with no element divisible by an adjacent element.

1, 2, 2, 12, 20, 180, 648, 5784, 36936, 485040, 2034876, 33492048, 373375392, 4974252864, 52465459392, 1067273994240, 11538658531008, 260749481442240