The sequence is

Where, for .

Consider and

Consider .

Substitute and in the recursive sequence.

Consider .

Substitute and in the above recursive sequence.

Consider .

Substitute and in the above recursive sequence.

Therefore, and

Hence, the sequence will be repeated first six terms.

Sum of six terms is

The sum of six terms is zero.

Hence the sum of first sixty terms also zero.

The sum of first sixty terms is zero.