My brother lost the combination to his safe the other day and while he could recall the first sets of digits he could not for the life of him recall the last. Knowing that my brother is a fiend with patterns I sought to assist him. Can you help too?
19, 13, 16, 11, 13, 9, ==??==
10.
19 - 6 = 13, 13 + 3 = 16
16 - 5 = 11, 11 + 2 = 13
13 - 4 = 9, 9 + 1 = 10
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