Better variable names to start with.

This prints information about the structure of the shape you want
Code:
for ( row = 0, items_on_row = 4 ; row < 3 ; row++, items_on_row-- ) {
  printf("Row %d will have %d numbers\n", row, items_on_row );
  for ( n = 0 ; n < items_on_row ; n++ ) {
    printf("%d, ", n );
  }
  printf("\n");
}
Now, think about how you can replace printing n, with printing some other value derived from the variables you have.