There are 994 possible positions to consider.

The probability that it is in any specific one of them is (1/6)^7 = .00000357224

The probability that it is not in any specific one of them is 1-.00000357224 = .99999642776

The probability that it is in none of them is (.99999642776)^994 = .996455

The probability that it is somewhere within the sequence is 1-.996455 = .003545

This is approximate.

The full exact answer, I think, is 1-(1-(1/6)^7)^994