for n being triangular number holds
( n, 0 are_congruent_mod 10 or n,1 are_congruent_mod 10 or n,3 are_congruent_mod 10 or n,5 are_congruent_mod 10 or n,6 are_congruent_mod 10 or n,8 are_congruent_mod 10 )