1、3^21=10460353203。

2、演算过程：

3^21=3*3^20

=3*(3^2)^10

=3*9^10

=3*(10-1)^10

=3*[10^10-C(10,1)*10^9+C(10,2)*10^8-C(10,3)*10^7+……+C(10,8)*10^2-C(10,9)*10+1]

=3*[45*10^8-120*10^7+210*10^6-252*10^5+210*10^4-120*10^3+45*10^2-10*10+1]

=3*[(33+2.1-0.252)*10^8+(21-1.2)*10^5+4500-100+1]

=3*[34.848*10^8+19.8*10^5+4500-100+1]

=3*[34848*10^5+19.8*10^5+4500-100+1]

=3*[34867.8*10^5+4401]

=104603.4*10^5+13203

=10460353203