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The sequence of numbers a1, a2, a3, . . . , an,

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The sequence of numbers a1, a2, a3, . . . , an, [#permalink] New post 16 Aug 2018, 13:43
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The sequence of numbers a1, a2, a3, . . . , an, . . . is defined by an=an-1 + n for each integer n ≥ 2 and a1=1. What is the value of a49?
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Re: The sequence of numbers a1, a2, a3, . . . , an, [#permalink] New post 16 Aug 2018, 22:17
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a2=a1+2
a3=a2+3
-------
-------
an=an-1+n

sum them up => an=a1+2+3+...+n
Since a1=1 => an=n(1+n)/2 => a49=1225
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Re: The sequence of numbers a1, a2, a3, . . . , an, [#permalink] New post 17 Aug 2018, 04:09
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natamiracle wrote:
The sequence of numbers a1, a2, a3, . . . , an, . . . is defined by an=an-1 + n for each integer n ≥ 2 and a1=1. What is the value of a49?



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Re: The sequence of numbers a1, a2, a3, . . . , an,   [#permalink] 17 Aug 2018, 04:09
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