156 Let $A=\{(x, y) \mid x, y \in \mathbf{N}, 1 \leqslant x . y \leqslant 20\}, B=\{(x, y) \mid x, y \in \mathbf{N}$, $2 \leqslant x, y \leqslant 19\} . A$ consists of points that are colored either red or blue, with 219 points colored red, 180 of which are included in $B$. The four corner points $(1,1),(1,20),(20,1),(20,20)$ are all colored blue. Adjacent grid points are connected by red, blue, or black segments according to the following rules: if both points are red, they are connected by a red segment; if both points are blue, they are connected by a blue segment; if one point is red and the other is blue, they are connected by a black segment. If there are 237 black segments of length 1, then the number of blue segments of length 1 is $\qquad$
156 233. Region $A$ contains a total of 400 grid points, of which 219 are red points and 181 are blue points. The perimeter of $A$ has 76 points, including 39 red points and 37 blue points (including the four corner points). Inside $B$, there are 144 blue points. Each of the four corner points of $A$ extends 2 line segments, each of the other boundary points extends 3 line segments, and each point inside $B$ extends 4 line segments. Therefore, the total number of line segments extending from blue points is
$$
2 \times 4 + 3 \times 33 + 4 \times 144 = 683 \text{ (segments). }
$$

Among these, there are 237 black segments, and each blue segment is counted twice, so the number of blue segments is
$$
(683 - 237) \div 2 = 446 \div 2 = 233 \text{ (segments). }
$$