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LV 1
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· rec-1
Recursive Sequences · Unrolling recursions
AMC 10 style
●●●○○ 6/10
~3 min
⏱ 0:00
Define
f
(
1
)
=
1
f(1) = 1
f
(
1
)
=
1
and
f
(
n
)
=
f
(
n
−
1
)
+
n
f(n) = f(n-1) + n
f
(
n
)
=
f
(
n
−
1
)
+
n
for
n
≥
2
n \ge 2
n
≥
2
. What is
f
(
20
)
f(20)
f
(
20
)
?
recursion
triangular-numbers
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Hint 1 of 3
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