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A172089
Triangle T(n,m) = n!/(m!!*(n-m)!!) read by rows, where (.)!! = A006882(.) are double factorials.
1
1, 1, 1, 1, 2, 1, 2, 3, 3, 2, 3, 8, 6, 8, 3, 8, 15, 20, 20, 15, 8, 15, 48, 45, 80, 45, 48, 15, 48, 105, 168, 210, 210, 168, 105, 48, 105, 384, 420, 896, 630, 896, 420, 384, 105, 384, 945, 1728, 2520, 3024, 3024, 2520, 1728, 945, 384, 945, 3840, 4725, 11520, 9450, 16128, 9450, 11520, 4725, 3840, 945
OFFSET
0,5
COMMENTS
Row sums are {1, 2, 4, 10, 28, 86, 296, 1062, 4240, 17202, 77088, ...}.
FORMULA
T(n,m) = A000142(n)/(A006882(m)*A006882(n-m)).
EXAMPLE
Triangle begins
1;
1, 1;
1, 2, 1;
2, 3, 3, 2;
3, 8, 6, 8, 3;
8, 15, 20, 20, 15, 8;
15, 48, 45, 80, 45, 48, 15;
48, 105, 168, 210, 210, 168, 105, 48;
105, 384, 420, 896, 630, 896, 420, 384, 105;
384, 945, 1728, 2520, 3024, 3024, 2520, 1728, 945, 384;
945, 3840, 4725, 11520, 9450, 16128, 9450, 11520, 4725, 3840, 945;
MAPLE
A172089 := proc(n, m)
factorial(n)/doublefactorial(m)/doublefactorial(n-m) ;
end proc:
seq(seq(A172089(n, m), m=0..n), n=0..10) ; # R. J. Mathar, Oct 11 2011
MATHEMATICA
binomialn[n_, k_] = n!/(Factorial2[n-k]*Factorial2[k]); Table[binomialn[n, k], {n, 0, 10}, {k, 0, n}]//Flatten
PROG
(PARI)
f2(n) = prod(i=0, (n-1)\2, n - 2*i );
T(n, k) = n!/(f2(k)*f2(n-k));
for(n=0, 10, for(k=0, n, print1(T(n, k), ", "))) \\ G. C. Greubel, Dec 05 2019
(Magma)
F2:=func< n | &*[n..2 by -2] >;
[Factorial(n)/(F2(k)*F2(n-k)): k in [0..n], n in [0..10]]; // G. C. Greubel, Dec 05 2019
(Sage)
def T(n, k): return factorial(n)/((k).multifactorial(2)*(n-k).multifactorial(2))
[[T(n, k) for k in (0..n)] for n in (0..10)] # G. C. Greubel, Dec 05 2019
CROSSREFS
Sequence in context: A039913 A108617 A092683 * A057475 A024376 A230128
KEYWORD
nonn,tabl,easy
AUTHOR
Roger L. Bagula, Jan 25 2010
STATUS
approved