A072007 a(0) = 0; for n>=1, a(n)=least nonnegative integer x such that |x-a(n-1)|>=n and x is not a(k) for any k<n.

0, 1, 3, 6, 2, 7, 13, 4, 12, 21, 5, 16, 28, 8, 22, 37, 9, 26, 44, 10, 30, 51, 11, 34, 58, 14, 40, 67, 15, 45, 75, 17, 49, 82, 18, 53, 89, 19, 57, 96, 20, 61, 103, 23, 68, 113, 24, 71, 119, 25, 76, 127, 27, 80, 134, 29, 85, 142, 31, 90, 150, 32