\(P=\left(5+5^2\right)+5^2\left(5+5^2\right)+....+5^{98}\left(5+5^2\right)=30\left(1+5^2+....+5^{98}\right)\) chia hết cho 30
=>P chia hết cho 30
=>đpcm
P= 51+52+53+..........+598+599+5100
P= (51+52)+(53+54)+..........+(599+5100)
P= (51+52)(1+52+..........+597+598+599)
P=30.(1+52+..........+597+598+599)chia hết cho 30