A049879 a(n)=|j-k|, where u(n)=u(j)+u(k) is the unique sum of Ulam numbers described in A002859.

1, 2, 3, 2, 2, 3, 4, 6, 4, 7, 9, 7, 10, 12, 12, 14, 12, 15, 17, 17, 19, 17, 20, 22, 5, 26, 25, 19, 27, 16, 29, 13, 31, 33, 33, 31, 8, 6, 37, 3, 39, 19, 40, 42, 42, 44, 4, 46, 6, 48, 48, 8, 50, 11, 53, 53, 55, 53