Intereting Posts

If $x$ is a positive integer such that $x(x+1)(x+2)(x+3)+1=379^2$, find $x$
3rd iterate of a continuous function equals identity function
Noether's definition of right and left ideals?
Deciding whether two metrics are topologically equivalent in the space $C^1()$
$\int_{0}^{\infty} f(x) \,dx$ exists. Then $\lim_{x\rightarrow \infty} f(x) $ must exist and is $0$. A rigorous proof?
Cardinality of the set of hyperreal numbers
Defining the multidimensional Riemann Integral as a limit of certain sums
Find $v_p\left(\binom{ap}{bp}-\binom{a}{b}\right)$, where $p>a>b>1$ and $p$ odd prime.
Proving that $n|m\implies f_n|f_m$
Prove if an element of a monoid has an inverse, that inverse is unique
how many permutations of {1,2,…,9}
Top 3 of 4 Dice Rolls
Precise statement of exponent laws for real numbers
How many non-isomorphic binary structures on the set of $n$ elements?
Counting number of solutions with restrictions

I have a vector of numbers that looks like this:

```
[1, 2, 3, 4, 5]
```

For every number the vector, I would like to multiply each number by every other number and find the sum:

```
1*1 + 1*2 + 1*3 + 1*4 + 1*5 + 2*1 + 2*2 + 2*3 + 2*4 + 2*5 + ... + 5*5
```

How can I write this in math notation?

- Etymology of Tor and Ext
- Is arrow notation for vectors “not mathematically mature”?
- Much less than, what does that mean?
- Understanding the differential $dx$ when doing $u$-substitution
- Strangest Notation?
- Why do we use “congruent to” instead of equal to?

- What does $dx$ mean?
- Proper notation for distinct sets
- Is there a difference between $y(x)$ and $f(x)$
- History of notation: “!”
- Why do we assume principal root
- Is there a symbol to mean 'this is undefined'?
- Funny translations of mathematical words
- Who introduced the notation $x^2$?
- Why does the sign $\times$ vanish in mathematical expressions?
- Notation for function $ + \rightarrow \times $

$\sum_{i=1}^5 \sum_{j=1}^5 ij$.

However, you can also give the array $v$ values $v_i$ other than the index $i$. Then you would write:

$\sum_{i=1}^5 \sum_{j=1}^5 v_iv_j$.

- Is there a general formula for this integral?
- Folner sets in a quotient of a f.g. amenable group
- Optimal strategy for this Nim generalisation?
- What are the applications of finite calculus
- Tensors as mutlilinear maps
- How to compute Riemann-Stieltjes / Lebesgue(-Stieltjes) integral?
- How does one get the formula for this bijection from $\mathbb{N}\times\mathbb{N}$ onto $\mathbb{N}$?
- Calculate integral with cantor measure
- Proving uniform continuity on an interval
- Integrating Reciprocals of Polynomials
- Show that the cardinality of $\mathbb N$ is the same as the cardinality of $\mathbb N \times \mathbb N$
- What is the difference between topological and metric spaces?
- Linear independence of function vectors and Wronskians
- On continuously uniquely geodesic space
- Real projective plane: $f_*$ isomorphism $\implies f$ surjective