In this paper, some formulae for computing the numbers of spanning trees of the corona and the join of graphs are deduced.
Partially filled \(6 \times 6\) Sudoku grids are categorized based on the arrangement of the values in the first three rows. This categorization is then employed to determine the number of \(6 \times 6\) Sudoku grids.
Stankova and West proved in 2002 that the patterns \( 231 \) and \( 312 \) are shape-Wilf-equivalent. Their proof was nonbijective. We give a new characterization of \( 231 \) and \( 312 \) avoiding full rook placements and use this to give a simple bijection that demonstrates the shape-Wilf-equivalence.