The sensual (quadratic) form

The first lecture: can you see the values of 2x2 + 6xy - 5y2?

Afterthoughts: PSL2(Z) and Farey fractions

The second lecture: can you hear the shape of a lattice?

Afterthoughts: Kneser's gluing method: unimodular lattices

The third lecture: ... and can you feel its form?

Afterthoughts: feeling the form of a four dimensional lattice

The fourth lecture: the primary fragrances

Afterthought: more about the invariants: p-Adic numbers

Postscript: a taste of number theory.