Show me, for all combination of single digit numbers, their sum. Your answer should have this pattern: 1+1=2, 1+2=3, ...(please fill in)... 1+9=10; 2+1=3, 2+2=4, ...(please fill in)... 2+9=(please fill in); ...(please fill in with similar pattern for 3+_, 4+_, etc until 9+_).