THERE ARE N NECKLACES. IN THE FIRST NECKLACE, THERE ARE 5 BEADS...

2. - ĐỀ THI TOÁN QUỐC TẾ PMWC VÒNG ĐỒNG ĐỘI 2. - ĐỀ THI TOÁN QUỐC TẾ PMWC VÒNG ĐỒNG ĐỘI
Toán ĐỀ THI TOÁN QUỐC TẾ PMWC VÒNG ĐỒNG ĐỘI
2. There are n necklaces. In the first necklace, there are 5 beads, in the secondnecklace, there are 7 beads, and in the i-th necklace there are i beads more thanthe (i－1)st necklace for i2. Find the total number of beads in these nnecklaces.

Answer： beads

2009 AsiaInter-CitiesTeenagersMathematics Olympiad

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