A059513 Variation of Boustrophedon transform applied to 1,1,1,1,... Fill an array by diagonals, in alternating directions. The first entry is 1 each time. For the next element of a diagonal, add to the previous element the elements of the row and the column the new element is in. The final element of each diagonal gives a(n).

1, 2, 6, 23, 116, 736, 5659, 50796, 521040, 6006587, 76874524, 1081439062, 16586149365, 275442822510, 4924040788654