**Abstract**

*This work shows the possibility and applicability of the methodological approach of the ancient mathematicians to the questions raised by scientists relatively recently. The concept of figurate numbers is being applied to the problem of periodicity in the microcosm.*

*It is should be noted that the Pythagorean approach demonstrates the principle of simplicity, or the Principle of Parsimony in science.*

**Introduction**

The mathematical study of figurate numbers is said to have originated with Pythagoras, possibly based on Babylonian or Egyptian precursors. Generating whichever class of figurate numbers the Pythagoreans studied using gnomons is also attributed to Pythagoras.

**Gnomon**

A gnomon [ˈnoʊmɒn] NO-mon, from Greek γνώμων, gnōmōn, literally “one that knows or examines”, is the part of a sundial that casts the shadow. The term has come to be used for a variety of purposes in mathematics and other fields.

Hero of Alexandria (also known as Heron of Alexandria c. 10 – c. 70 AD) defined the gnomon as that form which, when added to some form, results in a new form, similar to the original.

**Non-minimal ****1D**** gnomon ****– frame**

The available literature says nothing about how many gnomon variations a figure can have. For a rectangle, including square, a minimal gnomon is L-shaped figure.

But the frame figure can also serve as gnomon for the rectangle.

The dimension of the gnomon is one less than the dimension of the figure itself. Gnomons for one-dimensional line (string of beads) are the points with zero dimension. Gnomon for a two-dimensional figure is a one-dimensional figure. Gnomon for volumetric figure is a plane figure.

**Non-minimal 2D gnomon – shell**

One can offer the concept of volume figurate number shell as the non-minimal gnomon. Shell then is a gnomon the shape of which is similar to the whole volumetric figure, but it is a hollow figure.

**Tetrahedron**

Consider a tetrahedron.

VolumeOfTheTetrahedron_{n} = (n(n+1)(n+2))/6 = 1, 4, 10, 20, 35, 56, 84, 120, 165, … ;

n = 1, 2, 3, … . n – length of the edge of the figure.

If we limit the number of all possible gnomons varieties by monolayer figures, one can count 4 kinds of gnomons:

1) triangle, 2) bent square, 3) trihedral cap, 4) shell.

One of the four possible sequences of tetrahedron shells is:

ShellOfTheTetrahedron= 2*(2*1^{2 }+ 2*2^{2}), 2*(2*3^{2 }+ 2*4^{2}), 2*(2*5^{2 }+ 2*6^{2}), …=

= 20, 100, 244, ….

Theorem:

*In terms of figurate numbers, one can construct a sequence of tetrahedra, the shells of which are equal to the double sum of two consecutive double squares of natural numbers. What is the point of such construction?*

Described structure of repeating doubled squares corresponds the structure of the table of the periodic law of elements.

Some scientists pay tribute to the table proposed by the French scholar Janet.

The length of the period in the periodic law, as is well known, is equal to 2n^{2}.

Periods of equal length are encountered twice in the table.

**Our proposition**

Three-dimensional table of the periodic law can be constructed in the form of a tetrahedron having an inner order. A comparison of the tetrahedron shells and the table of elements shows, that one tetrahedron shell corresponds to 4 periods of the 2D table.

It was also shown previously that the electron shells in the atoms and square gnomons are isomorphic [1].

Note that any modification of the periodic law table is abstract duality. On the one hand, it is simply an ordered list of existing or hypothetical elements. On the other hand, the table reflects the structural characteristics of the nucleus and electron shells of the atom. So, the number of balls in the model corresponds to the number of protons in the nucleus and electrons in orbitals. With a certain degree of abstraction our figures can be considered as a model of the atom.

**REFERENCES**

Weise, D. (2003): The Pythagorean approach to the problems of periodicity in chemistry and nuclear physics, In: Progress in Theoretical Chemistry and Physics, Vol.12, Advanced Topics in Theoretical Chemical Physics, Edited by Jean Maruany, Roland Lefebvre, and Erkki J. Brändas ISBN: 978-90-481-6401-1 (Print) 978-94-017-0635-3 (Online).