Let n = a positive integer.

Suppose you choose n distinct points on a line. The distance between

any pair of points is irrelevant.

A "curve" is either:

1) an individual point

2) a set of at least two points

3) an individual line segment

4) a set of at least two line segments

5) some combination of the above

I will label the points with A, B, C, ..., Y, Z, AA, AB, ..., and so on

as needed, consecutively from left to right, as we see them on

the screen.

If a line segment contains more than two points (recall that these are

discrete), then they will be labeled with only their endpoints. Each

"curve" in a list will be separated by a comma. The ordering in the

list is irrelevant.

**The topic in this post involves the unordered listing and number of**

**the total of discrete "curves" in two dimensions for n distinct points,**

**where n is greater than or equal to one.**

Examples:

--------------

n = 1

<----------------- A ---------------->

List: {A}

Total: 1

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n = 2

<-------------- A ----------- B ------------->

List: {A}, {B}, {A, B}, {AB}

Total: 4

**Note: Here, you cannot have {A, AB}, {B, AB}, or {A, B, AB},**

**because neither point A nor point B is isolated once you**

**identify AB as a line segment in the set.**

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n = 3

<-------- A -------- B -------------- C ----------->

List of points only: {A}, {B}, {C}, {A, B}, {A, C}, {B, C}, {A, B, C}

List of line segments only: {AB}, {BC}, {AC}

List of points and line segments mixed: {A, BC}, {AB, C}

Total: 12

**Note: Here, you cannot have {B, AC}, because point B is not**

**an isolated point. It is part of line segment AC, and AC has**

**already been listed.**

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Puzzle: Compute the total number of "curves" for n = 4.**

*** Optional additional question: If you continue on getting

totals for n = 5, 6, 7, 8, ..., you will get a sequence that might

suggest a pattern to you.

As with all sequences, there are an infinite number of pos-

sibilities for a formula. However, there is a formula that I have

in mind. Whatever formula you get, **do not** attempt to

prove it. Just type the formula in your reply.