[tex]\bf \begin{array}{ll} term&\stackrel{a(n-1)-3}{value}\\ \cline{1-2} a(1)&-6\\ a(2)&a(2-1)-3\\ &a(1)-3\\ &-6-3\\ &-9 \blacktriangleleft\\ a(3)&a(3-1)-3\\ &a(2)-3\\ &-9-3\\ &-12 \blacktriangleleft\\ a(4)&a(4-1)-3\\ &a(3)-3\\ &-15 \blacktriangleleft\\ a(5)&a(5-1)-3\\ &a(4)-3\\ &-18 \blacktriangleleft \end{array}[/tex]
