What is the sum of the first 28 terms in the following sequence? 1, 1, 2, 1, 3, 2, 1, 4, 3, 2, 1, 5, 4, 3, 2, …

The sequence groups are: (1), (1,2), (1,3,2), (1,4,3,2), (1,5,4,3,2), (1,6,5,4,3,2), (1,7,6,5,4,3,2)... Group k has k terms. Sum of k terms in group k = 1+2+...+k = k(k+1)/2. Cumulative terms: group 1=1, 2=3, 3=6, 4=10, 5=15, 6=21, 7=28. So first 28 terms = sum of groups 1 to 7 = 1+3+6+10+15+21+28 = 84.