Answer:
aₙ = 6 + 7n
Step-by-step explanation:
20 - 13 = 27 - 20 = 34 - 27 = 7
It is an arithmetic sequence with common difference of 7
a₁ = 13
a₂ = 20 = 13 + (2 -1 )*7
a₃ = 27 = 13 + (3 - 1)*7
a₄ = 34 = 13 + (4 - 1)*7
...
aₙ = 13 + (n - 1)*7 = 13 + 7n - 7 = 6 + 7n
ao
aₙ = 6 + 7n
