[tex]\displaystyle\\3^{21}-3\times\Big(3^2\times3^3\Big)^4+7^0 =\\\\=3^{21}-3\times\Big(3^{2+3}\Big)^4+7^0 =\\\\=3^{21}-3\times\Big(3^5\Big)^4+7^0 =\\\\=3^{21}-3\times3^{5\times4}+7^0 =\\\\=3^{21}-3\times3^{20}+7^0 =\\\\=3^{21}-3^{20+1}+7^0 =\\\\=3^{21}-3^{21}+7^0 =0+1=\boxed{\bf1}[/tex]