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A203901
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a(n)=f(a(n-1)+1,a(n-2)+1,a(n-3)), where f(x,y,z)=yz+zx+xy and (a(1),a(2),a(3))=(0,0,1).
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2
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0, 0, 1, 2, 6, 31, 302, 11706, 3919531, 47073195302, 185055980038616706, 8711901623180875318209094531, 1612189902974799120179526719227635256224945302
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OFFSET
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1,4
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COMMENTS
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For a guide to related sequences, see A203761.
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LINKS
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MATHEMATICA
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a[1] = 0; a[2] = 0; a[3] = 1;
a[n_] := SymmetricPolynomial[2, {1 + a[n - 1], 1 + a[n - 2], a[n - 3]}]
Table[a[n], {n, 1, 16}] (* A203901 *)
nxt[{a_, b_, c_}]:={b, c, Total[Times@@@Subsets[{a, b+1, c+1}, {2}]]}; NestList[nxt, {0, 0, 1}, 15][[All, 1]] (* Harvey P. Dale, Nov 01 2022 *)
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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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