How to calculate the largest eigenvalue and its eigenvector of a 20*20 matrix more quickly?

Actually, the matrix is an adjacency matrix of a network. The code is:

A1 = GridGraph({20, 20}, PlotLabel -> "20*20 nodes", 
VertexLabels -> "Name")
A = AdjacencyMatrix(A1);

I want to calculate the eigenvalue of A and its eigenvector.
I have tried the normal function such as Eigenvalues and Eigenvectors. But it need much time and may not get a result(my laptop have not complete the calculation yet.)
The code is:

(Lambda) = N(Eigenvalues(Normal(A), 1))((1));
uA = N(Eigenvectors(Normal(A), 1))((1));

I want to know whether there is a method or parameter to reduce the time.