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A122021
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a(n) = a(n-2) - (n-1)*a(n-3), with a(0) = 0, a(1) = 1, a(2) = 2.
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4
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0, 1, 2, 1, -1, -7, -6, -1, 43, 47, 52, -383, -465, -1007, 4514, 5503, 19619, -66721, -73932, -419863, 1193767, 1058777, 10010890, -25204097, -14340981, -265465457, 615761444, 107400049, 7783328783, -17133920383, 4668727362
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OFFSET
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0,3
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LINKS
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MAPLE
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a:= proc(n) option remember;
if n < 3 then n
else a(n-2)-(n-1)*a(n-3)
fi;
end proc;
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MATHEMATICA
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a[0]=0; a[1]=1; a[2]=2; a[n_]:= a[n]= a[n-2] - (n-1)*a[n-3]; Table[a[n], {n, 0, 30}]
RecurrenceTable[{a[0]==0, a[1]==1, a[2]==2, a[n]==a[n-2]-(n-1)a[n-3]}, a, {n, 30}] (* Harvey P. Dale, Apr 29 2022 *)
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PROG
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(PARI) my(m=30, v=concat([0, 1, 2], vector(m-3))); for(n=4, m, v[n] = v[n-2] - (n-2)*v[n-3]); v \\ G. C. Greubel, Oct 06 2019
(Magma) I:=[0, 1, 2]; [n le 3 select I[n] else Self(n-2) - (n-2)*Self(n-3): n in [1..30]]; // G. C. Greubel, Oct 06 2019
(Sage)
def a(n):
if (n<3): return n
else: return a(n-2) - (n-1)* a(n-3)
(GAP)
a:= function(n)
if n<3 then return n;
else return a(n-2) - (n-1)*a(n-3);
fi;
end;
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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