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A186826 Riordan array (s(x),x*S(x)) where s(x) is the g.f. of the little Schroeder numbers A001003, and S(x) is the g.f. of the large Schroeder numbers A006318. 6

%I #19 Mar 11 2023 08:13:59

%S 1,1,1,3,3,1,11,11,5,1,45,45,23,7,1,197,197,107,39,9,1,903,903,509,

%T 205,59,11,1,4279,4279,2473,1061,347,83,13,1,20793,20793,12235,5483,

%U 1949,541,111,15,1,103049,103049,61463,28435,10717,3285,795,143,17,1,518859,518859,312761,148249,58351,19199,5197,1117,179,19,1

%N Riordan array (s(x),x*S(x)) where s(x) is the g.f. of the little Schroeder numbers A001003, and S(x) is the g.f. of the large Schroeder numbers A006318.

%C Reverse of A144944. Inverse of A186827.

%H Reinhard Zumkeller, <a href="/A186826/b186826.txt">Rows n = 0..125 of triangle, flattened</a>

%F Riordan array ((1+x+sqrt(1-6*x+x^2))/(4*x), (1-x-sqrt(1-6*x+x^2))/2).

%F Sum_{k=0..n} T(n,k) = A010683(n).

%F Sum_{k=0..floor(n/2)} T(n-k, k) = A186828(n).

%F R(n,k) = k*Sum_{i=0..n-k} (A001003(i)/(n-i))*Sum_{m=0..n-k-i} binomial(n-i,m)*binomial(2*(n-i)-m-k-1, n-i-1), k>0, R(n,0) = A001003(n). - _Vladimir Kruchinin_, Mar 09 2011

%F Sum_{k=0..n} (-1)^k*T(n, k) = A239204(n-2). - _G. C. Greubel_, Mar 11 2023

%e Triangle begins

%e 1;

%e 1, 1;

%e 3, 3, 1;

%e 11, 11, 5, 1;

%e 45, 45, 23, 7, 1;

%e 197, 197, 107, 39, 9, 1;

%e 903, 903, 509, 205, 59, 11, 1;

%e 4279, 4279, 2473, 1061, 347, 83, 13, 1;

%e 20793, 20793, 12235, 5483, 1949, 541, 111, 15, 1;

%e 103049, 103049, 61463, 28435, 10717, 3285, 795, 143, 17, 1;

%e 518859, 518859, 312761, 148249, 58351, 19199, 5197, 1117, 179, 19, 1;

%e Production matrix of this triangle begins

%e 1, 1;

%e 2, 2, 1;

%e 2, 2, 2, 1;

%e 2, 2, 2, 2, 1;

%e 2, 2, 2, 2, 2, 1;

%e 2, 2, 2, 2, 2, 2, 1;

%e 2, 2, 2, 2, 2, 2, 2, 1;

%e 2, 2, 2, 2, 2, 2, 2, 2, 1;

%e 2, 2, 2, 2, 2, 2, 2, 2, 2, 1;

%e For instance, 107=1*45+2*23+2*7+2*1.

%t t[_, 0]=1; t[p_, p_]:= t[p, p]= t[p, p-1]; t[p_, q_]:= t[p, q]= t[p, q -1] + t[p-1, q] + t[p-1, q-1];

%t Table[t[p, q], {p,0,10}, {q,p,0,-1}]//Flatten (* _Jean-François Alcover_, Jul 16 2019 *)

%o (Haskell)

%o a186826 n k = a186826_tabl !! n !! k

%o a186826_row n = a186826_tabl !! n

%o a186826_tabl = map reverse a144944_tabl

%o -- _Reinhard Zumkeller_, May 11 2013

%o (SageMath)

%o @CachedFunction

%o def t(n,k):

%o if (k<0 or k>n): return 0

%o elif (k==0): return 1

%o elif (k<n-1): return t(n,k-1) + t(n-1,k) + t(n-1,k-1)

%o else: return -t(n,n-2)

%o def A186826(n,k): return t(n+2,n-k)

%o flatten([[A186826(n,k) for k in range(n+1)] for n in range(13)]) # _G. C. Greubel_, Mar 11 2023

%Y Cf. A001003, A006318, A010683 (row sums), A144944 (row reverse), A186827 (inverse), A186828 (diagonal sums), A239204.

%K nonn,easy,tabl

%O 0,4

%A _Paul Barry_, Feb 27 2011

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)