DAY 466  MIND TICKLER
 
From Dell Penny Press Variety Puzzles
February, 2019

Find the missing number (?) and the next two numbers in the sequence:

5, 8, 13, 12, 7, 10, ?, 9 ........

Answer:

The missing number is 8. Starting from the third number, each number is equal to the sum of the digits of the previous two numbers. For example,  5+8=13,  8+1+3=12,  etc. 

The next number would be 17 (8+9), followed by 17 again (9+1+7).