I would like to ask prawn: for the sequence 1,2,4,7,11,16,22,29 --- how to find the sum of the first n terms?

I would like to ask prawn: for the sequence 1,2,4,7,11,16,22,29 --- how to find the sum of the first n terms?

Sequence 1, 2, 4, 7, 11, 16, 22, 29 The difference between the two adjacent terms in is 1, 2, 3, 4, 5, 6, 7 It is an arithmetic sequence, so the original sequence 1, 2, 4, 7, 11, 16, 22, 29 The general formula of second order arithmetic sequence is: x0dan = a1 + (n-1) (a2-a1) + (n-1) (n-2) D2 / 2; x0d = 1 + (n-1) + (n-1) (n-2) / 2; x0d = (2 + 2n-2 + n ^ 2-3n + 2) / 2; x0d = (n ^ 2-N + 2) / 2; the summation formula of x0d is: x0dsn = n + n (n-1) / 2 + n (n-1) (n-2) / 6