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A152751
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3 times octagonal numbers: 3*n*(3*n-2).
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20
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0, 3, 24, 63, 120, 195, 288, 399, 528, 675, 840, 1023, 1224, 1443, 1680, 1935, 2208, 2499, 2808, 3135, 3480, 3843, 4224, 4623, 5040, 5475, 5928, 6399, 6888, 7395, 7920, 8463, 9024, 9603, 10200, 10815, 11448, 12099, 12768, 13455
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OFFSET
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0,2
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COMMENTS
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a(n) also can be represented as n concentric triangles (see example). - Omar E. Pol, Aug 21 2011
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LINKS
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FORMULA
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EXAMPLE
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Illustration of initial terms as concentric triangles:
.
. o
. o o
. o o
. o o
. o o o o
. o o o o o o
. o o o o o o
. o o o o o o
. o o o o o o o o o
. o o o o o o o o o o o o
. o o o o o o
. o o o o o o o o o o o o o o o o o o
. o o
. o o o o o o o o o o o o o o
.
. 3 24 63
(End)
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MATHEMATICA
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PROG
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CROSSREFS
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Cf. numbers of the form n*(n*k-k+6))/2, this sequence is the case k=18: see Comments lines of A226492.
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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