We can consider this as an arithmetic progression (A.P)
Therefore AP : 2+4+6+... upto n
For finding the sum of all the numbers in an AP there is a formula. The formula is
Sum = \frac{n}{2}*[2a + (n-1)d]
        where n = number of elements of the AP
                 a = first element of the AP
                 d = the common difference (ie the 1st element - 2nd element)
sum = \frac{n}{2}*[2*2 + (n-1)*2]
sum = n[n+1]

mean = sum of all elemets ÷ total number of elements
mean = n(n+1)÷n
mean = n+1

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