2171313

Appears in sequences

• Number of mappings from n points to themselves with in-degree <= 2.at n=18A006961
• Number of zero-sum nX4 -2..2 arrays with every element equal to at least one horizontal or vertical neighbor.at n=3A201887
• T(n,k)=Number of zero-sum nXk -2..2 arrays with every element equal to at least one horizontal or vertical neighbor.at n=24A201888