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A309341
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a(n) = Sum_{j=1..n*(n-1)} (n*j mod (n+j)).
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1
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0, 2, 19, 67, 185, 373, 742, 1249, 2053, 3111, 4672, 6467, 9113, 12164, 16124, 20862, 26801, 33376, 41889, 51089, 62342, 75007, 89949, 106152, 125610, 146699, 170757, 197305, 227912, 259643, 297469, 336895, 381304, 429869, 483295, 539575, 603725, 670931, 745068, 823421, 910928
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OFFSET
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1,2
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COMMENTS
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Sum goes up to j = n*(n-1) because n*j == j-n*(n-1) (mod (n+j)) for j >= n*(n-1).
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LINKS
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FORMULA
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Conjecture: a(n) ~ c*n^4 where c = 0.32246....
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EXAMPLE
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For k = 3, 1*3 = 3 == 3 (mod 4), 2*3 = 6 == 1 (mod 5), 3*3 = 9 == 3 (mod 6), 4*3 = 12 == 5 (mod 7), 5*3=15 == 7 (mod 8), 6*3 = 18 == 0 (mod 9), so a(3) = 3+1+3+5+7 = 19.
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MAPLE
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f:= k -> add((k*j) mod (k+j), j=1..k*(k-1)-1):
map(f, [$1..30]);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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