#### If the sum of the first 6 terms of an A.P. is 36 and that of the first 16 terms is 256, find the sum of the first 10 terms.

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#### Show that a_{1}, a_{2}, a_{3}, … form an A.P. where a_{n} is defined as a_{n} = 3 + 4n. Also, find the sum of the first 15 terms.

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