Find the 20^th term of the given sequence. 12, 19, 29, 42, ...

The sequence is 12, 19, 29, 42. The differences are 7, 10, 13, which is an arithmetic progression with d=3. The n-th term is a_n = a_1 + sum of (7 + (i-1)3). For n=20, a_20 = 12 + (19/2)(2*7 + 19*3) = 12 + 9.5(14 + 57) = 12 + 674.5, which suggests a calculation error in the sequence or formula. Re-calculating: a_n = 1.5n^2 + 2.5n + 8. For n=20, 1.5(400) + 2.5(20) + 8 = 600 + 50 + 8 = 658.