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A055437
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a(n) = 10*n^2+n.
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6
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11, 42, 93, 164, 255, 366, 497, 648, 819, 1010, 1221, 1452, 1703, 1974, 2265, 2576, 2907, 3258, 3629, 4020, 4431, 4862, 5313, 5784, 6275, 6786, 7317, 7868, 8439, 9030, 9641, 10272, 10923, 11594, 12285, 12996, 13727, 14478, 15249, 16040, 16851, 17682, 18533
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OFFSET
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1,1
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COMMENTS
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Number of edges in the join of the complete 4-partite graph of order 4n and the cycle graph of order n, K_n,n,n,n * C_n. - Roberto E. Martinez II, Jan 07 2002
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LINKS
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FORMULA
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G.f.: x*(11 + 9*x) / (1 - x)^3.
a(n) = Sum_{i=0..2*n} (-1)^i*(2*n+i)^2.
a(n) = Sum_{i=1..2*n} (-1)^i*(4*n+i)^2. (End)
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3) for n>3.
a(n) = (1/5) * Sum_{i=0..10*n} i. (End)
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EXAMPLE
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From the third formula: a(8) = 648 = 16^2 -17^2 +18^2 ... +30^2 -31^2 +32^2 = -33^2 +34^2 -35^2 ... +46^2 -47^2 +48^2.
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MAPLE
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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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STATUS
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approved
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