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Recursion
easy
0:00.0
A sequence
a
n
=
a
n
−
1
+
n
a_n = a_{n-1} + n
a
n
=
a
n
−
1
+
n
has
a
1
=
1
a_1=1
a
1
=
1
. What is
a
3
a_3
a
3
?
A
3
B
4
C
6
D
7
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