LOG#158. Ramanujan’s equation.

Hi, everyone! I am back, again! And I have some new toys in order to post faster (new powerful plugin). Topic today: Ramanujan!


Why Ramanujan liked the next equation?

(1)   \begin{equation*} 2^n-7=x^2 \end{equation*}

This equation can be rewritten as follows

(2)   \begin{equation*} 2^{p+3}-7=x^2=(2n-1)^2 \end{equation*}

The full set of solutions in terms of the pair (p,n) can be found to be:

(3)   \begin{equation*} S=\left[(0,0),(1,2),(2,3),(4,6),(12,91)\right] \end{equation*}

If we put


the solutions are obvious and, the substitution allows to write


as the transformed equation


Therefore, the Ramanujan’s “seven equation” is deeply related with the following problem:

“(…)Find and calculate the values of the pair (p,n) such as a Mersenne prime number is a triangular number(…)”

Currently, we do know that the above equation has the previously quoted 5 solutions. Curiously, Ramanujan also loved the number 5 (not only the number 7) since he liked the golden ration, continuous fractions and related topics. In fact, the Rogers-Ramanujan identities are important in Mathematics and Physics.
In particular, we also observe:

(4)   \begin{equation*}2^p-1=(n-1)n/2=\begin{pmatrix} n\\ 2\end{pmatrix}=\sum_{k=1}^{n-1}k\end{equation*}

This equation has the next set of solutions:











These relationships are connected (secretly) with the Clifford algebras and orthogonal groups in the following way.

1st. Trivial and nullity

    \[ C(0)\rightarrow O(0)\]

2nd. Trivial as well

    \[ C(1)\rightarrow O(1)\]

3rd. First non trivial result (known to mathematical and physicists)

    \[ C(2)\rightarrow O(3)\]

4th. Non trivial case (a little bit unknown case, linking rotations in six dimensions with the Clifford algebra of spacetime):

    \[ C(4)\rightarrow O(6)\]

5th. Mysterious case (not easily found in the literature), highly non trivial and VERY unknown to physicists and mathematicians (to my knowledge)

    \[ C(12)\rightarrow O(91)\]


Two recent news I liked very much:

1) Pentagraphene: a new graphene-like structure and material.


2) A new type of bond beyond those you know from high school (ionic, covalent and metallic): THE VIBRATIONAL BOND (found in bromine-muonium systems Br-Mu-Br).


See you later, I wish!





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