Sequence - 1 / 3,1 / 6, - 1 / 9,1 / 12.. a general term formula sequence 2, - 6,81, - 54. A general term formula What do you think?

Sequence - 1 / 3,1 / 6, - 1 / 9,1 / 12.. a general term formula sequence 2, - 6,81, - 54. A general term formula What do you think?

an=[1/(3n)]*(-1)^(n)