# What is the sum of all the integers less than 700 that are divisible by 3and 7?

Thus the A.P. has a = 21 ; d = 42 - 21 = 21 ; a

_{n}= 693

Now, a

_{n}= a + (n - 1)d

693 = 21 + (n - 1)(21)

672 = (n - 1)(21)

n - 1 = 32

n = 33

Now, S

_{n}= (n/2)(a + a

_{n})

S

_{n}= (33/2)(21 + 693)

S

_{n}= (33/2)(714)

S

_{n}= 33 × 357

S

_{n}= 11781

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