\(M=1.2.3+2.3.4+3.4.5+...+47.48.49\)
\(4M=1.2.3.4+2.3.4.\left(5-1\right)+3.4.5.\left(6-2\right)+...+47.48.49.\left(50-46\right)\)
\(=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+...+47.48.49.50-46.47.48.49\)
\(=47.48.49.50\)
\(M=\frac{47.48.49.50}{4}=1381800\)