Add sequences of numbers in the 60's

1. Choose a 2-digit number in the 60's. To add all the 60's
   from 60 up through this number and down from it:
2. Square the 2nd digit of the number
   (keep the carry)   _ _ X
3. The number of terms is 2 x the 2nd digit + 1.
4. Multiply the number of terms by 6 (+ carry)   X X _

   Example:

1. If the 2-digit number in the 60's selected is 63:
   (60 + 61 + 62 + 63 + 62 + 61 + 60)
2. Square the 2nd digit of the number:
   3 x 3 = 9   _ _ 9
3. No. of terms = 2 x 2nd digit + 1:
   2 x 3 + 1 = 7
4. 6 x no. of terms: 6 x 7 = 42   4 2 _
5. So the sum of the sequence is 429.

   See the pattern?

1. If the 2-digit number in the 60's selected is 68:
   (60 + 61 + 62 + ... + 68 + 67 + ... 62 + 61 + 60)
2. Square the 2nd digit of the number:
   8 x 8 = 64 (keep carry 6)   _ _ 4
3. No. of terms = 2 x 2nd digit + 1:
   2 x 8 + 1 = 17
4. 6 x no. of terms: 6 x 17 + 6 = 42 + 1 =
   102 + 6 = 108   1 0 8 _
5. So the sum of the sequence is 1084.