Sum of this sequence is equal to the number of permutation matrices with determinant +1 = 5!/2 = 60. For number matrices with determinant = -1 see A171809.
Table of n, a(n) for n=1..5.
a(1)=1 because there is only one matrix whose first power is the identity matrix (this is the identity matrix itself).
Cf. A171806, A171809.
Sequence in context: A031112 A219394 A330522 * A134617 A113529 A214410
Adjacent sequences: A171805 A171806 A171807 * A171809 A171810 A171811
Artur Jasinski, Dec 18 2009