Your answer is correct according to your method. - difference in sequence 1, x, 6 where x = previous number +1

Their answer is correct according to their method. - difference in sequence 1, x, y where x = previous number + 1 as in your case but y = last digit of previous number in sequence.

Sequences like this have an infinite number of "correct" answers.

Their answer is correct according to their method. - difference in sequence 1, x, y where x = previous number + 1 as in your case but y = last digit of previous number in sequence.

Sequences like this have an infinite number of "correct" answers.