Integrate[1/n,n]

DSolve[{n'[t]==r n[t],n[0]==n0},n,t]

Plot[3.1 Exp[2.1 t],{t,0,2}]

Manipulate[Plot[3.1 Exp[r t],{t,0,2}],{r,-5,5}]

Manipulate[Plot[n0 Exp[r t],{t,0,tmax},Frame->True,FrameLabel->{"time","Density"}],{n0,0.1,10},{r,-5,5},{tmax,1,10}]

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(* This is a comment *)
f[x_]:=3 x+2

f[2]

Geometric Model

?f

f[n_]:=1.6 n

f[4.1]

f[6.56]

f[10.496]

f[f[f[4.1]]]

NestList[f,4.1,3]

ListLinePlot[NestList[f,4.1,3]]