1, 1, 4, 10, 26, 59, 140, 307, 684, 1464, 3122, 6500, 13426, 27248, 54804, 108802, 214071, 416849, 805124, 1541637, 2930329, 5528733, 10362312, 19295226, 35713454, 65715094, 120256653, 218893580, 396418699, 714399381, 1281403841, 2287986987, 4067428375, 7200210523, 12693890803, 22290727268, 38993410516, 67959010130, 118016656268, 204233654229, 352245710866, 605538866862, 1037668522922, 1772700955975, 3019333854177, 5127694484375, 8683676638832, 14665233966068, 24700752691832, 41495176877972, 69531305679518
Offset: 0
Examples for n=2 and n=3.
a(2) = 4: 2; 11 where the first 1 is at the origin and the second 1 is in the x, y or z direction.
a(3) = 10: 3; 21 where the 2 is at the origin and the 1 is on the x, y or z axis; 111 (a row of 3 ones on the x, y or z axes); and three 1's with one 1 at the origin and the other two 1's on two of the three axes.
From _Gus Wiseman_, Jan 22 2019: (Start)
The a(1) = 1 through a(4) = 26 solid partitions, represented as chains of chains of integer partitions:
((1)) ((2)) ((3)) ((4))
((11)) ((21)) ((22))
((1)(1)) ((111)) ((31))
((1))((1)) ((2)(1)) ((211))
((11)(1)) ((1111))
((2))((1)) ((2)(2))
((1)(1)(1)) ((3)(1))
((11))((1)) ((21)(1))
((1)(1))((1)) ((11)(11))
((1))((1))((1)) ((111)(1))
((2))((2))
((3))((1))
((2)(1)(1))
((21))((1))
((11))((11))
((11)(1)(1))
((111))((1))
((2)(1))((1))
((1)(1)(1)(1))
((11)(1))((1))
((2))((1))((1))
((1)(1))((1)(1))
((1)(1)(1))((1))
((11))((1))((1))
((1)(1))((1))((1))
((1))((1))((1))((1))
(End)
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