Consecutive numbers:
S=N(N+1)/2
*N includes the first element that is why we add 1 at the end
Even numbers:
N= ((Last - First)/2) +1
S= N(N+1)
Odd numbers:
N=((Last-First)/2)+1
S= N^2
Other numbers:
S=Avg * N
N=((Last-First)/Spacing)+1
