S_{30} = \frac{30}{2} \left(2 \cdot 2 + (30 - 1) \cdot 3 \right) = 15 \left(4 + 29 \cdot 3 \right) = 15 (4 + 87) = 15 \cdot 91 = 1365

Sun, 03 May 2026 14:53:54 +0000

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