If a, b, c and d are positive integers such that $${{\mathtt{a}}}^{{\mathtt{b}}}{\mathtt{\,\times\,}}{{\mathtt{c}}}^{{\mathtt{d}}} = {{\mathtt{2}}}^{{\mathtt{10}}}{\mathtt{\,\times\,}}{{\mathtt{7}}}^{{\mathtt{9}}}$$, what is the least possible value of a + b + c + d ?