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A051873
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21-gonal numbers: a(n) = n*(19n - 17)/2.
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13
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0, 1, 21, 60, 118, 195, 291, 406, 540, 693, 865, 1056, 1266, 1495, 1743, 2010, 2296, 2601, 2925, 3268, 3630, 4011, 4411, 4830, 5268, 5725, 6201, 6696, 7210, 7743, 8295, 8866, 9456, 10065, 10693, 11340, 12006, 12691, 13395, 14118
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OFFSET
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0,3
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COMMENTS
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Sequence found by reading the line from 0, in the direction 0, 21, ... and the parallel line from 1, in the direction 1, 60, ..., in the square spiral whose vertices are the generalized 21-gonal numbers. - Omar E. Pol, Jul 18 2012
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REFERENCES
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Albert H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, p. 189.
E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 6.
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LINKS
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FORMULA
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Product_{n>=2} (1 - 1/a(n)) = 19/21. - Amiram Eldar, Jan 22 2021
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MAPLE
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MATHEMATICA
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PolygonalNumber[21, Range[0, 40]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 22 2016 *)
Table[n*(19*n - 17)/2, {n, 0, 100}] (* Robert Price, Oct 11 2018 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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