392n^4 + 168n^3 + 168n^2 +72n

392n^4 + 168n^3 + 168n^2 +72n

8n(49n^3+21n^2 + 21n+9)
grouping gives
8n(7n^2(7n+3)+3(7n+3))
8n(7n+3)(7n^2+3)