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Search: id:A164823
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A164823 Irregular triangle read by rows, listing the values of cos(2*pi/k) mod j, for j >= 2 and k = 1:j-1. +0
7
1, 1, 1, 2, 1, 1, 3, 1, 1, 1, 4, 1, 2, 1, 4, 1, 1, 2, 4, 5, 1, 1, 2, 3, 4, 5, 1, 1, 1, 6, 1, 3, 1, 6, 1, 1, 3, 4, 6, 1, 1, 3, 5, 7, 1, 1, 2, 3, 4, 5, 6, 7, 1, 1, 3, 5, 7, 1, 1, 1, 8, 1, 4, 7, 1, 3, 6, 8, 1, 1, 2, 4, 5, 7, 8, 1, 1, 3, 6, 8, 1, 1, 4, 6, 9, 1, 7, 1, 4, 5, 6, 9, 1, 1, 2, 3, 4, 6, 7, 8, 9, 1, 1, 4, 5 (list; graph; listen)
OFFSET

1,4

LINKS

C. H. Gribble, Flattened irregular triangle, for j = 2:100 and k = 1:j-1.

EXAMPLE

The values are listed horizontally in increasing order for each (j, k) under the column headed "cos(2*pi/k) mod j".

The column headed "nov" is the number of values. The values read downwards form A164822.

I call "cos(x) mod j" the "Discrete Cosine of x modulo j".

cos(2*pi/k) mod j can be calculated by expressing cos(2pi) as a polynomial P in cos(2pi/k), for which the coefficients are those of Chebyshev's T(n,x) polynomials (A053120), and then solving P - 1 = 0 mod j by trial and error.

...j.......k.....nov....cos(2*pi/k).mod.j

...2.......1.......1.......1

...3.......1.......1.......1

...........2.......2.......1.......2

...4.......1.......1.......1

...........2.......2.......1.......3

...........3.......1.......1

...5.......1.......1.......1

...........2.......2.......1.......4

...........3.......2.......1.......2

...........4.......2.......1.......4

...6.......1.......1.......1

...........2.......4.......1.......2.......4.......5

...........3.......1.......1

...........4.......5.......1.......2.......3.......4.......5

...........5.......1.......1

...7.......1.......1.......1

...........2.......2.......1.......6

...........3.......2.......1.......3

...........4.......2.......1.......6

...........5.......1.......1

...........6.......4.......1.......3.......4.......6

...8.......1.......1.......1

...........2.......4.......1.......3.......5.......7

...........3.......1.......1

...........4.......7.......1.......2.......3.......4.......5.......6.......7

...........5.......1.......1

...........6.......4.......1.......3.......5.......7

...........7.......1.......1

...9.......1.......1.......1

...........2.......2.......1.......8

...........3.......3.......1.......4.......7

...........4.......4.......1.......3.......6.......8

...........5.......1.......1

...........6.......6.......1.......2.......4.......5.......7.......8

...........7.......1.......1

...........8.......4.......1.......3.......6.......8

..10.......1.......1.......1

...........2.......4.......1.......4.......6.......9

...........3.......2.......1.......7

...........4.......5.......1.......4.......5.......6.......9

...........5.......1.......1

...........6.......8.......1.......2.......3.......4.......6.......7.......8.......9

...........7.......1.......1

...........8.......5.......1.......4.......5.......6.......9

...........9.......2.......1.......7

..11.......1.......1.......1

...........2.......2.......1......10

...........3.......2.......1.......5

...........4.......2.......1......10

...........5.......3.......1.......7.......9

...........6.......4.......1.......5.......6......10

...........7.......1.......1

...........8.......2.......1......10

...........9.......2.......1.......5

..........10.......6.......1.......2.......4.......7.......9......10

CROSSREFS

Cf. A164822, A164831, A164846, A165252.

Sequence in context: A167407 A051340 A165430 this_sequence A167269 A105535 A108888

Adjacent sequences: A164820 A164821 A164822 this_sequence A164824 A164825 A164826

KEYWORD

nonn,tabf

AUTHOR

Christopher Hunt Gribble (chris.eveswell(AT)virgin.net), Aug 27 2009

EXTENSIONS

Sequence corrected by Christopher Hunt Gribble (chris.eveswell(AT)virgin.net), Sep 10 2009

Minor edit by N. J. A. Sloane, Sep 13 2009

Minor edit by Christopher Hunt Gribble (chris.eveswell(AT)virgin.net), Oct 01 2009

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Last modified December 9 18:50 EST 2009. Contains 170568 sequences.


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