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%I #16 Jan 18 2024 09:57:12
%S 2,3,2,5,3,8,3,8,9,2,5,10,3,4,15,16,4,10,13,19,4,19,22,27,2,5,10,11,
%T 20,21,26,29,3,6,9,15,20,24,25,32,33,5,6,10,11,33,37,3,8,9,13,20,23,
%U 30,34,35,40,4,10,18,19,28,29,37,43
%N Irregular triangle read by rows: Nonexistent values of cos(2*Pi/k) mod j, for j >= 2 and 1 <= k <= j-1.
%C See A164823 for explanatory comment and the definition of "cos(x) mod j".
%H Christopher Hunt Gribble, <a href="/A165609/b165609.txt">Flattened irregular triangle, for 2 < j < 1000</a>.
%e The irregular triangle of numbers without empty rows is:
%e ..j....Nonexistent values of cos(2*Pi/k) mod j
%e ..4....2
%e ..5....3
%e ..7....2..5
%e .11....3..8
%e .13....3..8..9
%e .17....2..5.10
%e .19....3..4.15.16
%e .23....4.10.13.19
%e .29....4.19.22.27
%e .31....2..5.10.11.20.21.26.29
%e .37....3..6..9.15.20.24.25.32.33
%e .41....5..6.10.11.33.37
%e .43....3..8..9.13.20.23.30.34.35.40
%e .47....4.10.18.19.28.29.37.43
%Y Cf: A164823, A165252.
%K nonn,tabf
%O 1,1
%A _Christopher Hunt Gribble_, Sep 22 2009
%E Minor edits from _N. J. A. Sloane_, Sep 25 2009
%E Minor edit by _Christopher Hunt Gribble_, Oct 01 2009