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A227009
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Irregular triangle read by rows: T(n,k) is the number of partitions of an n X n square lattice into squares that contain k nodes unconnected to any of their neighbors, considering only the number of parts.
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2
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1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 2, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 4, 2, 2, 2, 2, 1, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 4, 3, 3, 4, 4, 4, 3, 4, 3, 2, 2, 2, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1
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OFFSET
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1,13
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COMMENTS
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The n-th row contains (n-1)^2 + 1 elements.
The irregular triangle is shown below.
\ k 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ...
n
1 1
2 1 1
3 1 1 0 0 1
4 1 1 1 1 2 0 0 0 0 1
5 1 1 1 1 2 1 1 1 0 1 0 0 0 0 0 0 1
6 1 1 1 1 2 2 2 2 3 4 2 2 2 2 1 0 2 0 0 ...
7 1 1 1 1 2 2 2 2 3 4 3 3 4 4 4 3 4 3 2 ...
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LINKS
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FORMULA
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It appears that T(n,k) = T(n-1,k), n odd, n > 1 and k = 0..(n-1)^2/4.
Sum_{k=0..(n-1)^2} T(n,k) = A034295(n).
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EXAMPLE
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For n = 6, there are 3 partitions that contain 8 isolated nodes, so T(6,8) = 3.
An m X m square contains (m-1)^2 isolated nodes.
Consider that each partition is composed of ones and zeros where a one represents a node with one or more links to its neighbors and a zero represents a node with no links to its neighbors. Then the 3 partitions are:
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 0 1 0 1 0 1 1 0 0 1 1 0 1 1 0 0 1 0 0 1
1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 0 0 1 0 0 1
1 0 1 0 1 0 1 1 1 1 1 1 0 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 0 1 0 1 1 1 1 1 1 0 1 0 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
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MAPLE
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b:= proc(n, l) option remember; local i, k, s, t;
if max(l[])>n then {} elif n=0 or l=[] then {0}
elif min(l[])>0 then t:=min(l[]); b(n-t, map(h->h-t, l))
else for k do if l[k]=0 then break fi od; s:={};
for i from k to nops(l) while l[i]=0 do s:=s union
map(v->v+x^(1+i-k), b(n, [l[j]$j=1..k-1,
1+i-k$j=k..i, l[j]$j=i+1..nops(l)]))
od; s
fi
end:
T:= n-> (w->seq(coeff(w, z, h), h=0..(n-1)^2))(add(z^add(
coeff(p, x, i)*(i-1)^2, i=2..degree(p)), p=b(n, [0$n]))):
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MATHEMATICA
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b[n_, l_List] := b[n, l] = Module[{i, k , s, t}, Which[Max[l] > n, {}, n == 0 || l == {}, {0}, Min[l] > 0, t = Min[l]; b[n-t, l-t], True, For[k = 1, k <= Length[l], k++, If[l[[k]] == 0, Break[]]]; s = {}; For[i = k, i <= Length[l] && l[[i]] == 0, i++, s = s ~Union~ Map[# + x^(1+i-k)&, b[n, Join[l[[1 ;; k-1]], Array[1+i-k&, i-k+1], l[[i+1 ;; Length[l]]]]]]]; s]]; T[n_] := Function[w, Table[Coefficient[w, z, h], {h, 0, (n-1)^2}]][Sum[ z^Sum[Coefficient[p, x, i]*(i-1)^2, {i, 2, Exponent[p, x]}], {p, b[n, Array[0&, n]]}]]; Table[T[n], {n, 1, 9}] // Flatten (* Jean-François Alcover, Jan 24 2016, after Alois P. Heinz *)
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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