I’m hopefully going to pass the halfway point on this year’s mathematics A-To-Z. This makes it a good time to panel for topics for the next several letters in the alphabet. It’s easier for me to keep my notes straight if you post requests as comments on this thread, but I’ll try to keep up if you do comment on other threads.

As ever, I’m happy to consider most mathematical topics, including ones that I’ve written about in the past if I think I can better an old essay. If there’s several suggestions for the same letter, I’ll pick the one that I think I can do most interestingly. If several seem interesting I might try rephrasing, if the subject allows for that.

And I do thank everyone who makes a suggestion, especially if it’s one that surprises me and that makes me learn something along the way.

Here’s the essays I’ve written in past years for the letters O through T.

### O.

**Orthogonal**(Summer 2015)**Orthonormal**(Leap Day 2016)**Osculating circle**(End 2016)**Open set**(Summer 2017)**Oriented Graph**(Fall 2018)

### P.

**Proper**(Summer 2015)**Polynomials**(Leap Day 2016)**Principal**(End 2016)**Prime number**(Summer 2017)**Pigeonhole principle**(Fall 2018)

### Q.

**Quintile**(Summer 2015)**Quaternion**(Leap Day 2016)**Quotient Groups**(End 2016)**Quasirandom Numbers**(Summer 2017)**Quadratic Equation**(Fall 2018)

### R.

**Ring**(Summer 2015)**Riemann Sphere**(Leap Day 2016)**Riemann sum**(End 2016)**Ricci Tensor**(Summer 2017)**Randomness**(Fall 2018)

### S.

**Step**(Summer 2015)**Surjective Map**(Leap Day 2016)**Smooth**(End 2016)**Sárközy’s Theorem**(Summer 2017)**Sorites Paradox**(Fall 2018)

### T.

**Tensor**(Summer 2015)**Transcendental Number**(Leap Day 2016)**Tree**(End 2016)**Topology**(Summer 2017)**Tiling**(Fall 2018)

T for Taylor series!

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Great thought! Thank you.

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Octagon or Operator

Platonic

Qualitative/Quantitative

Relatively Prime

Sample Space

Tangram

(Kind of a K-12 collection)

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Fantastic collection of topics though. Thank you!

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