# Four is the magic number [duplicate]

Can someone figure out the pattern? Each number always maps to another number, eventually getting to 4.

$1 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$2 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$3 \Rightarrow 5 \Rightarrow 4$

$4$

$5 \Rightarrow 4$

$6 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$7 \Rightarrow 5 \Rightarrow 4$

$8 \Rightarrow 5 \Rightarrow 4$

$9 \Rightarrow 4$

$10 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$11 \Rightarrow 6 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$12 \Rightarrow 6 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$

$13 \Rightarrow 8 \Rightarrow 5 \Rightarrow 4$

$14 \Rightarrow 8 \Rightarrow 5 \Rightarrow 4$

$15 \Rightarrow 7 \Rightarrow 5 \Rightarrow 4$

$16 \Rightarrow 7 \Rightarrow 5 \Rightarrow 4$

$17 \Rightarrow 9 \Rightarrow 4$

$18 \Rightarrow 8 \Rightarrow 5 \Rightarrow 4$

$19 \Rightarrow 8 \Rightarrow 5 \Rightarrow 4$

$20 \Rightarrow 6 \Rightarrow 3 \Rightarrow 5 \Rightarrow 4$