What is the next number of the following sequence - 69, 915, 515, 511, 17, ??

Answer 1

69, 915, 515, 511, 17, 78

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the last digit of previous number & sum of digits of that gives us a new number
69
9 (6+9)-> 915
5 (9+1+5)->515
5 (5+1+5)->511
1 (5+1+1)->17
7 (1+7)-> 78