Variance of first n natural numbers {1,2,...,n} = (n^2-1)/12. This is derived from Mean = (n+1)/2 and sum(i^2) = n(n+1)(2n+1)/6. For an AP {a, a+d, a+2d, ..., a+(n-1)d}: Var = d^2*(n^2-1)/12. The variance of an AP depends only on the common difference d and the number of terms n, not on the first term a (since shifting doesn't change variance). Example: Var({3,7,11,15,19}) = 4^2*(25-1)/12 = 162 = 32. For consecutive even or odd numbers, d=2: Var = 4(n^2-1)/12 = (n^2-1)/3.