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Use [n(n+1)/2]^2 for cubic summations.
Answer = [99 * 100 / 2]^2 - 2 * 2^3 * [49 * 50 / 2]^2.
= (99 x 50)^2 - 4(49 x 50)^2.
= 50^2 (99^2 - 98^2).
= (99 - 98)(99 + 98)50^2.
= 197 x 2500.
= 492500