f(4)=f(1+3)=f(1)+1-7=1+1-7=-5;
f(7)=f(4+3)=f(4)+4-7=-5+4-7=-8
f(10)=f(7+3)=f(7)+7-7=-8
f(13)=f(10+3)=f(10)+10-7=-8+10-7=-5
f(16)=f(13+3)=f(13)+13-7=-5+13-7=1
f(19)=f(16+3)=f(16)+16-7=1+9=10
f(22)=f(19+3)=f(19)+19-7=10+19-7=22
f(25)=f(22)+22-7=37
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