TeX source:

\mathrm{a}_{1}=5, \mathrm{a}_{2}=\mathrm{a}_{1}+3=5+3=8, \mathrm{a}_{3}=\mathrm{a}_{2}+3=(5+3)+3=11, \mathrm{a}_{4}=\mathrm{a}_{3}+3=(5+3)+3+3=14