Four Fours/Glossary

Glossary of Symbols for Four Fours

Symbols used in the Four Fours are defined as follows:

\(\ds . \dot 4\)

\(:=\)

\(\ds 0.44444 \ldots\)

$.4$ recurring, equal to $\dfrac 4 9$

\(\ds \sqrt 4\)

\(:=\)

\(\ds 2\)

square root of $4$

\(\ds 4!\)

\(:=\)

\(\ds 1 \times 2 \times 3 \times 4\)

$4$ factorial

\(\ds \map \Gamma 4\)

\(:=\)

\(\ds 1 \times 2 \times 3\)

gamma function of $4$

\(\ds a \uparrow b\)

\(:=\)

\(\ds a^b\)

Knuth uparrow notation

\(\ds \floor x\)

\(:=\)

\(\ds \text {largest integer not greater than $x$}\)

floor function of $x$

\(\ds \map \pi x\)

\(:=\)

\(\ds \text {number of primes less than $x$}\)

prime-counting function of $x$