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A111694
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a(1) = 1+2-3 = 0, a(2) = 4+5+6-7 = 8, a(3) = 8+9+10+11-12 = 26, a(4) = 13+14+15+16+17-18 = 57, ...
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2
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0, 8, 26, 57, 104, 170, 258, 371, 512, 684, 890, 1133, 1416, 1742, 2114, 2535, 3008, 3536, 4122, 4769, 5480, 6258, 7106, 8027, 9024, 10100, 11258, 12501, 13832, 15254, 16770, 18383, 20096, 21912, 23834, 25865, 28008, 30266, 32642, 35139, 37760
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = (n-1)*(n^2 + 5*n + 2)/2.
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MAPLE
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seq(sum(j, j=binomial(n+1, 2)+n-1..binomial(n+2, 2)+n-2) - binomial(n+2, 2)-n+1, n=1..50); # Emeric Deutsch, Aug 27 2005
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MATHEMATICA
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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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EXTENSIONS
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STATUS
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approved
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