A Gareth sequence is a sequence of numbers in which each number after the second
is the non-negative difference between the two previous numbers. For example, if a
Gareth sequence begins 15; 12, then
• the third number in the sequence is 15 − 12 = 3,
• the fourth number is 12 − 3 = 9,
• the fifth number is 9 − 3 = 6,
and so the resulting sequence is 15; 12; 3; 9; 6; : : : . If a Gareth sequence begins 10; 8,
what is the sum of the first 30 numbers in the sequence?