A141905 - OEIS

%I #35 Nov 28 2021 07:59:02

%S 1,1,1,1,4,1,1,9,6,1,1,16,24,8,1,1,25,70,40,10,1,1,36,165,160,60,12,1,

%T 1,49,336,525,280,84,14,1,1,64,616,1456,1120,448,112,16,1,1,81,1044,

%U 3528,3906,2016,672,144,18,1,1,100,1665,7680,11970,8064,3360,960,180,20,1

%N Triangle read by rows, T(n, k) = binomial(n, k)*A052509(n, k) for 0 <= k <= n.

%C Original definition: A skew trinomial summed triangular sequence of coefficients: T(n, k) = Sum_{j=0..k} n!/((n - k - j)!*j!*k!).

%C It is obscure how the above formula is used for the region where the sum reaches k > n-m, which needs a definition of the factorials at negative integer argument. If we trust the author's Mma implementation, Mma throws in some magic renormalization to cover these arguments. If we define, properly, t(n, k) = Sum_{j=0..n-k) n!/((n-k-j)!*j!*k!), then we recover just A038207. - _R. J. Mathar_, Feb 07 2014

%C Let p(n, k, j) = n!/((n-k-j)!*j!*k!), for j<=n-k and 0<= k <=n and p(n, k, j) = 0, for j > n-k and 0<= k <=n. It seems that T(n, k) coincides with Sum_{j=0..k} p(n, k, j). - _Luis Manuel Rivera Martínez_, Mar 04 2014

%H G. C. Greubel, <a href="/A141905/b141905.txt">Rows n = 0..50 of the triangle, flattened</a>

%F T(n, k) = Sum_{j=0..k} n!/((n - k - j)!*j!*k!).

%F G.f.: (2*x)/((3*x - 1)*sqrt(-4*x^2*y + x^2 - 2*x + 1) - 4*x^2*y + x^2 - 2*x +1). - _Vladimir Kruchinin_, Oct 05 2020

%F T(n, k) = binomial(n, k)*hypergeom([-k, -n + k], [-k], -1). - _Peter Luschny_, Nov 28 2021

%e Triangle begins as:

%e [0]  1;

%e [1]  1,   1;

%e [2]  1,   4,    1;

%e [3]  1,   9,    6,    1;

%e [4]  1,  16,   24,    8,     1;

%e [5]  1,  25,   70,   40,    10,    1;

%e [6]  1,  36,  165,  160,    60,   12,    1;

%e [7]  1,  49,  336,  525,   280,   84,   14,   1;

%e [8]  1,  64,  616, 1456,  1120,  448,  112,  16,   1;

%e [9]  1,  81, 1044, 3528,  3906, 2016,  672, 144,  18,  1;

%p A052509 := proc(n, k) option remember: if k = 0 or k = n then 1 else A052509(n-1, k) + A052509(n-2, k-1) fi end: T := (n, k) -> binomial(n, k)*A052509(n, k): seq(seq(T(n, k), k=0..n), n=0..10); # _Peter Luschny_, Nov 26 2021

%t T[n_, k_]:= Sum[n!/((n-k-j)!*j!*k!), {j,0,k}];

%t Table[T[n, k], {n, 0, 10}, {k,0,n}] // Flatten

%o (Magma) [Binomial(n,k)*(&+[Binomial(n-k,j): j in [0..k]]): k in [0..n], n in [0..12]]; // _G. C. Greubel_, Mar 29 2021

%o (Sage) flatten([[binomial(n,k)*sum(binomial(n-k,j) for j in (0..k)) for k in [0..n]] for n in [0..12]]) # _G. C. Greubel_, Mar 29 2021

%Y Row sums are A027914.

%Y Cf. A038207, A052509.

%K nonn,tabl

%O 0,5

%A _Roger L. Bagula_ and _Gary W. Adamson_, Sep 14 2008

%E Edited by _G. C. Greubel_, Mar 29 2021

%E New name by _Peter Luschny_, Nov 26 2021