1×1+2×2+3×3+…+1991×1991的末位数字是多少？8P7j9u4X(Q:Q,|'g3E9C;m/z3e2N8A
算式：提示5u4l6P/U3{8P7j9u4X(Q:Q,|'g3E9C;m/z3e2N8A
答：末位数字是6\+i1Z3Q0r0}8y。8P7j9u4X(Q:Q,|'g3E9C;m/z3e2N8A