# RPS #006 - Not so expert series problem

**Algebra**Level 3

Let \(T_{n}\) denotes the \(n^{th}\) term in triangle number series \((1,3,6,10,...)\) for every positive integers \(n\)

Consider two function of \(S_{n} = T_1 + T_2 + T_3 + ... + T_n\) and \(R_n = S_1 + S_2 + S_3 + ... + S_n\)

Find the value of \(R_{21}\)

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