If you are willing to take a little skewed view on the "triangle", it can also be written as:

1,2
1,3 2,3
1,4 2,4 3,4
1,5 2,5 3,5 4,5
1,6 2,6 3,6 4,6 5,6
1,7 2,7 3,7 4,7 5,7 6,7
[download]

Now former diagonals form lines/rows and in this presentation "x" is constant in columns and "y" is constant in rows.

The above output can be generated e. g. by the following obfu code oneliner:
Win command line here; change delimiter from double- to single-quotes for other shell, if applicable

perl -Mstrict -wle "$.++;print qq(@{[map qq{$_,$.}, 1..++$.-1]}) while $.<7"