If sum of n terms of a series is defined as Sn = n2 + n + 1, then find the 15th term of this series.
Explanation:
Sn = n2 + n + 1
Tn = Sn - Sn-1
∴ T15 = S15 - S14
⇒ T15 = (152 + 15 + 1) - (142 + 14 + 1)
⇒ T15 = 241 - 211 = 30.
Hence, 30.
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