imc

If we list the rows by iterations, then we get $1,2,3,4$ $6,7,8,9,10$ $13,14,15,16,17,18$ etc. so that the $500,000$th number is the $506$th number on the $997$th row because $4+5+6+\mathrm{7......}+999=499,494$. The last number of the $996$th row (when including the numbers skipped) is $499,494+(1+2+3+\mathrm{4.....}+996)=996,000$, (we add the $1-996$ because of the numbers we skip) so our answer is $996,000+506=\boxed{996,506}$.