Oh wait, maybe I haven't quite got this right. My n is the number in the sequence. If the n in the question refers to the actual even integer, then I would have to divide this by 2 to get the position in the sequence. In that case, the answer would be 7,019,850, as 5298 is the 2649th number in the sequence of even integers >0. In this case I concur with Gaetano.
f(n=2m) = S = 2+4+6+ ... +2m // by definition of f and change of variable, n= 2m = 2*(1 + 2 + 3 + ... + m) // common factor of 2 = 2(m*(m+1)/2) // by sum of the m first integers = m(m+1) // simplification = (n/2)((n/2)+1) // by our definition of m
2+4+6+8+10.....n then 2(1+2+3....n/2)...so sum of n/2 terms will be 2. (n/2(n/2 + 1)) /2 so after calculating we will get (n/2(n/2 + 1)) and so.... n. (n+2) /4......and if n is 5298 then sum will be 7,019,850.
