A181960 Number of distinct nonnegative integers that can be generated by an expression containing n binary operators (any of add, subtract, multiply and divide) whose operands are any integer between 1 and 9; parenthesis allowed.
9, 40, 156, 740, 3668, 16948, 77861, 379084, 1889419
Offset: 0
Examples
a(1)=40, the distinct values are: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 21 24 25 27 28 30 32 35 36 40 42 45 48 49 54 56 63 64 72 81