A129276 - OEIS

%I #15 Feb 28 2023 07:44:09

%S 1,1,1,1,2,1,1,8,8,1,1,42,106,42,1,1,241,1558,1558,241,1,1,1444,23589,

%T 53612,23589,1444,1,1,8867,360499,1747433,1747433,360499,8867,1,1,

%U 55320,5530445,54794622,111482424,54794622,5530445,55320,1

%N Triangle, read by rows, where T(n,k) is the coefficient of q^(nk-k) in the squared q-factorial of n.

%C Dual triangle is A129274.

%C Central terms form a bisection of A127728.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/q-Factorial.html">q-Factorial</a>.

%F T(n,k) = [q^(nk-k)] Product_{i=1..n} { (1-q^i)/(1-q) }^2 for n>0, with T(0,0)=1.

%F Row sums = (n!)^2/(n-1) for n>=2.

%e Definition of q-factorial of n:

%e faq(n,q) = Product_{k=1..n} (1-q^k)/(1-q) for n>0, with faq(0,q)=1.

%e Obtain row 4 from coefficients in the squared q-factorial of 4:

%e faq(4,q)^2 = 1*(1 + q)^2*(1 + q + q^2)^2*(1 + q + q^2 + q^3)^2

%e = (1 + 3*q + 5*q^2 + 6*q^3 + 5*q^4 + 3*q^5 + q^6)^2;

%e the resulting coefficients of q are:

%e [(1), 6, 19, (42), 71, 96, (106), 96, 71, (42), 19, 6, (1)],

%e where the terms enclosed in parenthesis form row 4.

%e Triangle begins:

%e 1;

%e 1, 1;

%e 1, 2, 1;

%e 1, 8, 8, 1;

%e 1, 42, 106, 42, 1;

%e 1, 241, 1558, 1558, 241, 1;

%e 1, 1444, 23589, 53612, 23589, 1444, 1;

%e 1, 8867, 360499, 1747433, 1747433, 360499, 8867, 1;

%e 1, 55320, 5530445, 54794622, 111482424, 54794622, 5530445, 55320, 1; ...

%t faq[n_, q_] := Product[(1-q^k)/(1-q), {k, 1, n}]; t[0, 0] = t[1, 0] = t[1, 1] = 1; t[n_, k_] := SeriesCoefficient[faq[n, q]^2, {q, 0, (n-1)*k}]; Table[t[n, k], {n, 0, 8}, {k, 0, n}] // Flatten (* _Jean-François Alcover_, Nov 26 2013 *)

%o (PARI) T(n,k)=if(n==0,1,polcoeff(prod(i=1,n,(1-x^i)/(1-x))^2,(n-1)*k))

%Y Cf. A129277 (column 1), A129278 (column 2); A127728 (central terms), related triangles: A129274, A128564, A008302 (Mahonian numbers).

%K nonn,tabl

%O 0,5

%A _Paul D. Hanna_, Apr 07 2007