Hobbymath's wanderings #16

Abelian_sandpile_model (Wikipedia).

Single source sandpile example.

Self-organized_criticality (Wikipedia).

Principle of least action (Wikipedia).

Stirling's approximation (Wikipedia).

Plate trick (Wikipedia).

Kronecker_delta function (Wikipedia).

Approximate formulas for some functions of prime numbers (pdf).

Wilson's theorem (Wikipedia).

Tetration (Wikipedia).

Some OEIS sequences where I added some comments in the past: [A235353][A054602][A061066][A024206][A117484][A004125][A039669][A049802][A198383][A002093][A129527][A106108].

Pappus of Alexandria.

Common derivatives and integrals (pdf).

Fermat's little theorem.

Von Mangoldt function (Wikipedia).

An infinite series of surprises (+plus magazine).

Farey sequence (Wikipedia).

Square-free integer (Wikipedia).

Radical of an integer (Wikipedia).

Law of noncontradiction (Wikipedia).

Parallel coordinates visualizing system (Wikipedia).

Visualization of Multi-variate Scientific Data (pdf).

Rotations in 4-dimensional Euclidean space (Wikipedia)

The tesseract (brief description).