Lecture 7: Counting and the natural numbers
Supplemental sources
History of irrational numbers
(book) A History of Pythagoreanism, edited by Carl A. Huffman (see Sixth-, fifth- and fourth-century Pythagoreans Leonid Zhmud, section 3)
Lecture 5: Sets, paradoxes, axioms and infinity
Supplemental sources
Infinity and the Hilbert hotel
How an Infinite Hotel Ran Out Of Room (YouTube video)
The Infinite Hotel Paradox - Jeff Dekofsky (YouTube video)
Gödel's incompleteness Theorem
Gödel's incompleteness Theorem - Numberphile (YouTube video)
Lecture 4: Introduction to Sets
Supplemental sources
Lecture 3: More on number systems and some modern perspectives
Supplemental sources
Working with numbers in other bases
Lecture 2: Number systems and the concept of number
Supplemental sources
Number systems and their history
(book) Numerical Notation, A Comparitive History, by Stephen Chrisomalis
(book) Number Words and Number Symbols, A Cultural History of Numbers by Karl Menninger
Color and language
(book) Through the Language Glass, Why the World Looks Different in Other Languages by Guy Deutscher
(book) You can also find interesting discussions in Chapters 1 and 3 of Reading: the Grand Illusion, How and Why People Make Sense of Print by Ken Goodman, Peter H. Fries, and Steven L. Strauss