Correction:
5+13+21+...+181
First term = 5
Common difference = 13-5 = 8
Last term = an = 181
⇛a+(n-1)d = 181
⇛5+(n-1)(8) = 181
⇛ 5+8n-8 = 181
⇛ 8n-3 = 181
⇛ 8n = 181+3
⇛ 8n = 184
⇛n = 184/8
⇛ n = 23
Sum of the first n terms = Sn = (n/2)(a+an)
Sum of 23 terms = S 23
⇛(23/2)(5+181)
⇛ (23/2)(186)
⇛23×93
⇛2139
