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tmua.me Extreme Set A Paper 2 · Q20

Paper 2Functions & graphsNumber & counting

A function ff maps every positive integer to a positive integer and satisfies

f(f(n))=n+4f(f(n))=n+4

for every positive integer nn.

How many different functions ff satisfy this condition?

A22
B33
C66
D1212
E2424
FInfinitely many

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