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0, 7, 15, 30, 46, 69, 93, 124, 156, 195, 235, 282, 330, 385, 441, 504, 568, 639, 711, 790, 870, 957, 1045, 1140, 1236, 1339, 1443, 1554, 1666, 1785, 1905, 2032, 2160, 2295, 2431, 2574, 2718, 2869, 3021, 3180, 3340, 3507, 3675, 3850
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OFFSET
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0,2
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COMMENTS
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Sequence found by reading the line from 0, in the direction 0, 7,... and the line from 15, in the direction 15, 46,..., in the square spiral whose vertices are the triangular numbers A000217.
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LINKS
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FORMULA
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Array read by rows: row n gives 8*n^2 + 7n, 8*(n+1)^2 - (n+1).
a(n) = (3-3*(-1)^n+14*n+8*n^2)/4. a(n) = 2*a(n-1)-2*a(n-3)+a(n-4). G.f.: x*(7+x)/((1-x)^3*(1+x)). [Colin Barker, Jul 22 2012]
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EXAMPLE
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Array begins:
0, 7
15, 30
46, 69
93, 124
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CROSSREFS
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Cf. A000217, A046092, A139274, A139278, A077221, A139591, A139592, A139593, A139595, A139596, A139598.
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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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