A375441 - OEIS

%I #12 Sep 12 2024 15:00:05

%S 1,1,3,27,520,17461,924123,72565316,8092491188,1237738519836,

%T 252223179026317,66826143258640668,22547253821858556366,

%U 9516722710620123685768,4947980149610424524104600,3126554347854062023615490499,2372761989077914432028426533800,2140079932579758851404630992687571

%N Expansion of g.f. A(x) satisfying 0 = Sum_{k=0..n} (-1)^k * binomial(3*n-2*k, k) * ([x^k] A(x)^n) for n >= 1.

%C Note that 0 = Sum_{k=0..n} (-1)^k * binomial(n+2*k, 3*k) * ([x^k] D(x)^n) for n >= 1 is satisfied by the function D(x) = 1 + x*D(x)^3 (g.f. of A001764), where coefficient [x^k] D(x)^n = binomial(n+3*k-1, k)*n/(n+2*k).

%H Paul D. Hanna, <a href="/A375441/b375441.txt">Table of n, a(n) for n = 0..200</a>

%F a(n) ~ c * d^n * n!^3 * n^alpha, where d = 0.1579852929267375678916376580224..., alpha = 2.6601429516008505168108..., c = 0.86048778713891683578001... - _Vaclav Kotesovec_, Sep 12 2024

%e G.f.: A(x) = 1 + x + 3*x^2 + 27*x^3 + 520*x^4 + 17461*x^5 + 924123*x^6 + 72565316*x^7 + 8092491188*x^8 + ...

%e RELATED TABLES.

%e The table of coefficients of x^k in A(x)^n begins:

%e   n=1: [1, 1,  3,  27,  520,  17461,  924123, ...];

%e   n=2: [1, 2,  7,  60, 1103,  36124, 1887017, ...];

%e   n=3: [1, 3, 12, 100, 1758,  56097, 2890755, ...];

%e   n=4: [1, 4, 18, 148, 2495,  77500, 3937572, ...];

%e   n=5: [1, 5, 25, 205, 3325, 100466, 5029880, ...];

%e   n=6: [1, 6, 33, 272, 4260, 125142, 6170284, ...];

%e   ...

%e from which we may illustrate the defining property given by

%e 0 = Sum_{k=0..n} (-1)^k * binomial(3*n-2*k, k) * ([x^k] A(x)^n).

%e Using the coefficients in the table above, we see that

%e   n=1: 0 = 1*1 - 1*1;

%e   n=2: 0 = 1*1 - 4*2 + 1*7;

%e   n=3: 0 = 1*1 - 7*3 + 10*12 - 1*100;

%e   n=4: 0 = 1*1 - 10*4 + 28*18 - 20*148 + 1*2495;

%e   n=5: 0 = 1*1 - 13*5 + 55*25 - 84*205 + 35*3325 - 1*100466;

%e   n=6: 0 = 1*1 - 16*6 + 91*33 - 220*272 + 210*4260 - 56*125142 + 1*6170284;

%e   ...

%e The triangle A193636(n,k) = binomial(3*n-2*k, k) begins:

%e   n=0: 1;

%e   n=1: 1, 1;

%e   n=2: 1, 4, 1;

%e   n=3: 1, 7, 10, 1;

%e   n=4: 1, 10, 28, 20, 1;

%e   n=5: 1, 13, 55, 84, 35, 1;

%e   n=6: 1, 16, 91, 220, 210, 56, 1;

%e   ...

%o (PARI) {a(n) = my(A=[1],m); for(i=1, n, A=concat(A, 0); m=#A-1;

%o A[#A] = sum(k=0, m, (-1)^(m-k+1) * binomial(3*m-2*k, k) * polcoef(Ser(A)^m, k) )/m ); A[n+1]}

%o for(n=0, 20, print1(a(n), ", "))

%Y Cf. A193636, A375440, A375450, A375451.

%K nonn

%O 0,3

%A _Paul D. Hanna_, Sep 11 2024