%!PS

% A number spiral (of the primes) as per http://numberspiral.com/
% 2005-11-28 by Charlie Loyd.
% Do not use for evil.


/paperx 8.5 72 mul def
/papery 11 72 mul def
paperx 2 div papery 2 div translate % center

% Letter-size paper at these settings holds about 200k; 10k looks fine:
/max 65336 def

/mark? { % n mark? boolean
	% Your filter here. This marks primes (the dumb but clear way).
	% Try, e.g., { 3 mod eq } for an interesting pattern.
	/n exch def
%	/goesinto false def
	n 1 eq { false } {
		n 2 mod 0 eq { n 2 eq } {
			/divide? false def
			3 2 n sqrt ceiling {
				n exch mod 0 eq
				{ /divide? true def exit }  if
			} for divide? not
		} ifelse
	} ifelse
} def

0 1 max {
	dup mark? {
		dup sqrt dup 360 mul dup rotate
		cvi 360 mod 360.0 div 1.0 1.0 sethsbcolor
		0 1 0 360 arc fill
		sqrt 360 mul neg rotate % bottleneck
	} if
} for

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