Where you factor mini-RSA semiprimes. The game tries to help you by augmenting your guesses with propagated constraints on other cells and prime digits that arise from a guess.

The multiplication tableaux is the regular long-multiplication tableaux, but rotated and with zeroes elided, because it produces, along with the fact that we pick "RSA primes" to be the same digit length, a nicer symmetric square.

To introduce more slack you can guess either the Big Blind (the prime factor digits), or the small blind (the half-product digits in the tableaux).

Even with the constraints, you might find that doing this "semiprime factoring" is surprisingly hard (if you do it without just writing a loop to find the answer).

Despite that, the visual presentation clearly indicates how the information is present in the product to yield the factors. It's just occluded by the tableaux's as-yet-unrevealed inner states. Each cell in the tableaux is the product of a distinct pairs of factor digits corresponding to the diagonals that meet at that cell. The cells are split into "quotient and remainder modulo radix" (hence the "half-product digits") because it's the, in this orientation, vertical columns of alternating, adjacent quotients and remainders which sum (with carry) to the digits of the product.

Only a small set of automated contraints are included in this game, but you can imagine others.