The sum of the first 20 terms of the sequence a (n) = 7n+2

A = 7n + 2

a₁ = 7*1 + 2 = 9

a₂ = 7*2 + 2 = 16

a₃ = 7*3 + 2 = 23

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a₂₀ = 7*20 + 2 = 142

This is an Arithmetic progression, a = 9, last term = 142

Sum of the 20 terms using: n/2 (a + l) where l = last term.

= 20/2 (9 + 142)

= 10 * 151

= 1510

Sum of the first 20 terms = 1510