Ramanujan's ternary quadratic form
is the algebraic expression $x^2 + y^2 + 10z^2$ with integral values for x, y and z.
Galway verified that there are only eighteen numbers less than $2*10^{10}$ not representable in the form $x^2 + y^2 + 10z^2$.
Based on Galway's computations, Ken Ono and K. Soundararajan formulated the following conjecture:

The odd positive integers which are not of the form $x^2 + y^2 + 10z^2$ are: 3, 7, 21, 31, 33, 43, 67, 79, 87, 133, 217, 219, 223, 253, 307, 391, 679, 2719.