how to calculate arithmetic sequences
Go online to this link and get the formula from there:
https://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
Look under "Summing an Arithmetic Series"
1+2+......+n=\(\frac{n(1+n)}{2}\)
1+(1+a)+(1+2a)+......+(1+na)=\(\frac{[1+(1+na)](x)}{2}=\frac{(x)(2+na)}{2}\)
where \(x=n+1\)
