Could anyone explain what the commands
\@tempcntb
\count@\@ne
\@curtab
For reference, I found them on How to produce a list of prime numbers in LaTeX
i do understand that i can create new counts with
\catcode`\@=11 %makeatletter
\newcount\@tempcntb
\newcount\@curtab
\catcode`\@=12 %makeatother
but i don't see it appear in the macro, so i don't really understand them.
You linked to the question but I assume you mean this code from my answer
\makeatletter
\def\primes#1#2{{%
\def\comma{\def\comma{, }}%
\count@\@ne\@tempcntb#2\relax\@curtab#1\relax
\@primes}}
\def\@primes{\loop\advance\count@\@ne
\expandafter\ifx\csname p-\the\count@\endcsname\relax
\ifnum\@tempcntb<\count@\else
\ifnum\count@<\@curtab\else\comma\the\count@\fi\fi\else\repeat
\@tempcnta\count@\loop\advance\@tempcnta\count@
\expandafter\let\csname p-\the\@tempcnta\endcsname\@ne
\ifnum\@tempcnta<\@tempcntb\repeat
\ifnum\@tempcntb>\count@\expandafter\@primes\fi}
\makeatother
\@tempcntb and \@currtab are scratch count registers that are already defined by latex so you do not need \newcount (the first one intented for temporary use like this, the second one less so, it is normally used by tabbing
\count@\@ne is primitive syntax which sets the counter to 1.
\@tempcntb is a scratch counter allocated by the LaTeX kernel, so it's always available.
It's similar for \count@, which uses \count255 and is historically a scratch register.
\@curtab is instead a counter used in the code for tabbing and should not be used otherwise. (Not a capital sin in the particular usage, but not good programming style nonetheless.)
The available scratch counters in LaTeX are
\count@
\@tempcnta
\@tempcntb
