\[\boxed{\text{1203\ (1203).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[n(n + 1)(n + 2)(n + 3) + 1 =\]
\[= n(n + 3)\left( n^{2} + 2n + n + 2 \right) + 1 =\]
\[= \left( n^{2} + 3n \right)\left( n^{2} + 2n + n + 2 \right) + 1 =\]
\[+ 1 = \left( n^{2} + 3n + 1 \right)^{2} - 1^{2} + 1 =\]
\[= \left( n^{2} + 3n + 1 \right)^{2} - 1 + 1 =\]
\[= \left( n^{2} + 3n + 1 \right)^{2}\ \]