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A300190
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Number of solutions to 1 +- 2 +- 3 +- ... +- n == 0 (mod n).
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9
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1, 0, 2, 4, 4, 0, 10, 32, 30, 0, 94, 344, 316, 0, 1096, 4096, 3856, 0, 13798, 52432, 49940, 0, 182362, 699072, 671092, 0, 2485534, 9586984, 9256396, 0, 34636834, 134217728, 130150588, 0, 490853416, 1908874584, 1857283156, 0, 7048151672, 27487790720
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OFFSET
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1,3
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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Solutions for n = 7:
--------------------------
1 +2 +3 +4 +5 +6 +7 = 28.
1 +2 +3 +4 +5 +6 -7 = 14.
1 +2 -3 +4 -5 -6 +7 = 0.
1 +2 -3 +4 -5 -6 -7 = -14.
1 +2 -3 -4 +5 +6 +7 = 14.
1 +2 -3 -4 +5 +6 -7 = 0.
1 -2 +3 +4 -5 +6 +7 = 14.
1 -2 +3 +4 -5 +6 -7 = 0.
1 -2 -3 -4 -5 +6 +7 = 0.
1 -2 -3 -4 -5 +6 -7 = -14.
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MAPLE
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b:= proc(n, i, m) option remember; `if`(i=0, `if`(n=0, 1, 0),
add(b(irem(n+j, m), i-1, m), j=[i, m-i]))
end:
a:= n-> b(0, n-1, n):
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MATHEMATICA
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b[n_, i_, m_] := b[n, i, m] = If[i == 0, If[n == 0, 1, 0], Sum[b[Mod[n + j, m], i - 1, m], {j, {i, m - i}}]];
a[n_] := b[0, n - 1, n];
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PROG
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(Ruby)
def A(n)
ary = [1] + Array.new(n - 1, 0)
(1..n).each{|i|
i1 = 2 * i
a = ary.clone
(0..n - 1).each{|j| a[(j + i1) % n] += ary[j]}
ary = a
}
ary[(n * (n + 1) / 2) % n] / 2
end
(1..n).map{|i| A(i)}
end
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CROSSREFS
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Number of solutions to 1 +- 2^k +- 3^k +- ... +- n^k == 0 (mod n): this sequence (k=1), A300268 (k=2), A300269 (k=3).
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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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