1. A set of mathematical blocks useful in teaching and learning mathematics, each of said blocks having a front face, a back face, and, with reference to its front face, a top edge, a right edge, a bottom edge, and a left edge, said set comprising in combination: a plurality of said blocks that are referred to as +1 blocks, each having on its front face four edge dimension indicia referred to as +1 dimensions adjacent to its top, right, bottom, and left edges, respectively, and having on its back face four edge dimension indicia referred to as -1 dimensions adjacent to its top, right, bottom, and left edges, respectively; a plurality of said blocks that are referred to as +X blocks each having on its front face two edge dimension indicia referred to as +X dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as +1 dimensions adjacent to its left and right edges, and having on its back face two edge dimension indicia referred to as -X dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as -1 dimension adjacent to its right and left edges, respectively; a plurality of said blocks that are referred to as +X.sup.2 blocks each having on its front face four edge dimension indicia referred to as +X dimensions adjacent to its top, right, bottom, and left edges, respectively, and having on its back face a plurality of edge dimension indicia referred to as -X dimensions adjacent to its top, right, bottom and left edges, respectively; a plurality of said blocks referred to as -1 blocks each having on its front face two edge dimension indicia referred to as -1 dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as +1 dimensions adjacent to its right and left edges, respectively, and having on its back face two edge dimension indicia referred to as +1 edge dimensions adjacent to its top and bottom edges, respectively, and two edge dimension indicia referred to as -1 edge dimensions adjacent to its left and right edges, respectively; a plurality of said blocks referred to as -X blocks each having on its front face two edge dimension indicia referred to as -X edge dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as +1 dimensions adjacent to its right and left edges and having on its back face two edge dimension indicia referred to as +X edge dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as -1 edge dimensions adjacent to its right and left edges; a plurality of said blocks referred to as -X.sup.2 blocks each having on its front face two edge dimension indicia referred to as -X edge dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as +X edge dimensions adjacent to its left and right edges and having on its back face two edge dimension indicia referred to as +X edge dimensions adjacent to its top and bottom edges and two edge dimension indicia referred to as -X edge dimensions adjacent to its right and left edges; each of said +1, +X, and +X.sup.2 blocks having at each of its edges and edge alignment means for effecting proper alignment of that edge with only one edge of any of the other blocks, the lengths of each of the edges of said blocks having a +1 edge dimension or a -1 edge dimension being equal, and the lengths of each of the edges of said blocks having a +X edge dimension or a -X edge dimension being equal, the edges with +X or -X edge dimensions being different in length than the edges having +1 or -1 edge dimensions, whereby various ones of said blocks can be arranged to form rectangles representing algebraic expressions wherein the sums of the dimension indicia of each side of the formed rectangle represent factors of the algebraic expression.