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A093118
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Triangle T read by rows: T(m,n) = number of convex polyominoes with an m+1 X n+1 minimal bounding rectangle, m > 0, n <= m.
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6
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5, 13, 68, 25, 222, 1110, 41, 555, 3951, 19010, 61, 1171, 11263, 70438, 329126, 85, 2198, 27468, 216618, 1245986, 5693968, 113, 3788, 59676, 579330, 4022546, 21832492, 98074332, 145, 6117, 118605, 1389927, 11462495, 72887139, 379145115, 1680306750
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OFFSET
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1,1
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LINKS
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FORMULA
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T(m,n) = ((m+n+m*n)*C(2*m+2*n, 2*m) - 2*m*n*C(m+n, m)^2)/(m+n), for m + n > 0.
T(m,n) = C(2*m+2*n,2*m) + ((2*m+2*n-1)/2)*C(2*m+2*n-2,2*m-1) - 2*(m+n-1) *C(m+n,m)*C(m+n-2,m-1), for m >= 0, n >= 0. - Günter Rote, Feb 12 2019
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EXAMPLE
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Triangle begins:
5,
13, 68,
25, 222, 1110,
41, 555, 3951, 19010,
61, 1171, 11263, 70438, 329126,
85, 2198, 27468, 216618, 1245986, 5693968,
...
This is the lower half of an infinite square table that is symmetric at the main diagonal (T(m,n)=T(n,m)).
For m=2 and n=1, the T(2,1)=13 polyominoes in a 3 X 2 rectangle are the five polyominoes
.
+---+---+---+ +---+ +---+---+
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+---+---+---+ +---+---+---+ +---+---+---+
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+---+---+---+ +---+---+---+ +---+---+
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+---+ +---+---+
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+---+---+---+ +---+---+---+
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+---+---+---+ +---+---+---+
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plus all their different horizontal and vertical reflections (1 + 2 + 2 + 4 + 4 = 13 polyominoes in total). (End)
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MAPLE
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T:= (m, n)-> (m+n+m*n)/(m+n)*binomial(2*m+2*n, 2*m)
-2*m*n/(m+n)*binomial(m+n, m)^2:
seq(lprint(seq(T(m, n), n=1..m)), m=1..10); # Alois P. Heinz, Feb 24 2019
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MATHEMATICA
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T[m_, n_] := (m+n+m n)/(m+n) Binomial[2m + 2n, 2m] - 2 m n/(m+n) Binomial[ m+n, m]^2;
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PROG
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(Sage)
def T(m, n):
w, h = m+1, n+1 # width and height
p = w+h # half the perimeter
return ( binomial(2*p-4, 2*w-2) + binomial(2*p-6, 2*w-3)*(p-5/2) - 2*(p-3)*binomial(p-2, w-1)*binomial(p-4, w-2) ) # Günter Rote, Feb 13 2019
(PARI) {T(n, k) = ((n+k+n*k)*binomial(2*n+2*k, 2*n) - 2*n*k*binomial(n+k, n)^2)/(n+k)};
for(n=1, 8, for(k=1, n, print1(T(n, k), ", "))) \\ G. C. Greubel, Feb 18 2019
(Magma) [[((n+k+n*k)*Binomial(2*n+2*k, 2*n) - 2*n*k*Binomial(n+k, n)^2)/(n+k): k in [1..n]]: n in [1..8]]; // G. C. Greubel, Feb 18 2019
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CROSSREFS
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Sums of T(m,n) with fixed sum m+n (including entries with n > m and the trivial ones: T(0,x)=T(y,0)=1), are A005436. - Günter Rote, Feb 12 2019
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KEYWORD
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AUTHOR
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STATUS
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approved
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