There is currently no known formula for determining the number of self-avoiding walks, although there are rigorous methods for approximating them.

There is no known general formula to compute the Frobenius number of numerical semigroups having embedding dimension three or more.

There is currently no known formula for the exact number of solutions.

Then from the known formulae you can calculate the basis vectors of the reciprocal lattice.

For prime n 1 (mod 8), however, there is no known formula.

The obscure McDonald's alter ego company was based on Sonneborn's unique even lesser known financial formula.

The inspiration for adopting the word entropy in information theory came from the close resemblance between Shannon's formula and very similar known formulae from thermodynamics.

The shape of an object might already be mathematically determined, but it may be too complex to use a known formula.

There is currently no known formula to compute the accessible information.

Moreover, he could recover the known formulas for four, six and eight squares although his method was quite different.