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COMMENT
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a(n) is the number of functions on a finite set {1,...,n} that are not composition powers of any other function or powers(>1) of itself.
Hard to compute for n>7, as the number of functions to test is n^n.
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EXAMPLE
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For n=2, the set is {1,2} and we have 4 functions: the constants 1 and 2, the identity, and the transposition. Any composition power of a constant function or of identity is the function itself. Odd composition powers of the transposition give the transposition. Thus all 4 functions are represented.
For n=3, the set is {1,2,3} and f:{1,2,3}->{1,1,2} can not be represented by composition powers of any other function, or powers of itself (as fof gives the constant function=1). There are 6 functions in this situation (similar).
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