The next term in the sequence, a 2 {\displaystyle a_{2}} , is 2 since the pairwise sums then are 2, 3 and 4, i.e., they are distinct. Then, a 3 {\displaystyle a_{3}} can't be 3 because there would be the non-distinct pairwise sums 1 + 3 = 2 + 2 = 4. We find then that a 3 = 4 {\displaystyle a_{3}=4} , with the pairwise sums being 2, 3, 4, 5, 6 and 8.