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A245312 G.f. A(x) satisfies: [x^(n+1)] A(x)^n = n^2 * ( [x^(n-1)] A(x)^n ) for n>=1. 3

%I #21 Jul 25 2014 08:05:27

%S 1,1,1,3,10,60,360,2940,24528,247968,2595920,31175496,389671200,

%T 5422095536,78605082528,1244958773760,20527083114496,364984417934400,

%U 6745106725383168,133136189132775360,2726068542132666240,59173740044950124160,1329834118793805335040,31493916740885086274304

%N G.f. A(x) satisfies: [x^(n+1)] A(x)^n = n^2 * ( [x^(n-1)] A(x)^n ) for n>=1.

%C Do the following limits exist? If so, what are the respective values?

%C (1) limit a(n)*sqrt(n+1)/(n+1)! ? (Value is near 0.263981 at n=400.)

%C (2) limit A245313(n)/A245312(n) ? (Value is near 2.721747 at n=400.)

%C Limit a(n)*sqrt(n+1)/(n+1)! = 0.264485471610277836304036..., limit A245313(n)/A245312(n) = e. - _Vaclav Kotesovec_, Jul 20 2014

%H Paul D. Hanna, <a href="/A245312/b245312.txt">Table of n, a(n) for n = 0..400</a>

%F Let A = A(x), the g.f. of this sequence, and G(x) = g.f. of A245313, then

%F (1) A(x) = 1 + x + x^2 + 3*x^3*A'/(A - x*A') + 2*x^4*(A')^2/(A - x*A')^2 + x^4*A^2*A''/(A - x*A')^3.

%F (2) A(x) = 1 + x + x^2 + 3*x^3*G'(x/A)/A^2 + x^4*G''(x/A)/A^3.

%F (3) G'(x/A) = A^2*A'/(A - x*A').

%F (4) G''(x/A) = 2*A^3*(A')^2/(A - x*A')^2 + A^5*A''/(A - x*A')^3.

%F (5) A(x) = G(x/A(x)) and G(x) = A(x*G(x)).

%F (6) A(x) = x / Series_Reversion(x*G(x)).

%e G.f.: A(x) = 1 + x + x^2 + 3*x^3 + 10*x^4 + 60*x^5 + 360*x^6 +...

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

%e n=1: [1, 1, 1, 3, 10, 60, 360, 2940, 24528, 247968, ...];

%e n=2: [1, 2, 3, 8, 27, 146, 869, 6780, 56116, 554232, ...];

%e n=3: [1, 3, 6, 16, 54, 270, 1576, 11796, 96441, 931539, ...];

%e n=4: [1, 4, 10, 28, 95, 448, 2548, 18344, 147631, 1395396, ...];

%e n=5: [1, 5, 15, 45, 155, 701, 3875, 26885, 212385, 1964755, ...];

%e n=6: [1, 6, 21, 68, 240, 1056, 5676, 38016, 294126, 2662868, ...];

%e n=7: [1, 7, 28, 98, 357, 1547, 8106, 52508, 397194, 3518354, ...];

%e n=8: [1, 8, 36, 136, 514, 2216, 11364, 71352, 527087, 4566528, ...];

%e n=9: [1, 9, 45, 183, 720, 3114, 15702, 95814, 690759, 5851051, 55951479]; ...

%e from which we can illustrate [x^(n+1)] A(x)^n = n^2*([x^(n-1)] A(x)^n):

%e n=1: [x^2] A(x) = 1 = 1*([x^0] A(x)) = 1*1 ;

%e n=2: [x^3] A(x)^2 = 8 = 2^2*([x^1] A(x)^2) = 2^2*2 ;

%e n=3: [x^4] A(x)^3 = 54 = 3^2*([x^2] A(x)^3) = 3^2*6 ;

%e n=4: [x^5] A(x)^4 = 448 = 4^2*([x^3] A(x)^4) = 4^2*28 ;

%e n=5: [x^6] A(x)^5 = 3875 = 5^2*([x^4] A(x)^5) = 5^2*155 ;

%e n=6: [x^7] A(x)^6 = 38016 = 6^2*([x^5] A(x)^6) = 6^2*1056 ;

%e n=7: [x^8] A(x)^7 = 397194 = 7^2*([x^6] A(x)^7) = 7^2*8106 ;

%e n=8: [x^9] A(x)^8 = 4566528 = 8^2*([x^7] A(x)^8) = 8^2*71352 ;

%e n=9: [x^10] A(x)^9 = 55951479 = 9^2*([x^8] A(x)^9) = 9^2*690759 ; ...

%e describing terms that lie along diagonals in the above table.

%e From the main diagonal in the above table, we may derive A245313:

%e [1/1, 2/2, 6/3, 28/4, 155/5, 1056/6, 8106/7, 71352/8, 690759/9, ...]

%e = [1, 1, 2, 7, 31, 176, 1158, 8919, 76751, ...].

%o (PARI) /* From: [x^(n-1)] A(x)^n = n^2*([x^(n+1)] A(x)^n) */

%o {a(n)=local(A=[1,1]);for(i=1,n,A=concat(A,0);m=#A-2;A[#A]=-Vec(Ser(A)^m*(1-m^2*x^2))[#A]/m);A[n+1]}

%o for(n=0,30,print1(a(n),", "))

%o (PARI) /* From differential equation: */

%o {a(n)=local(A=1+x,D=1);for(i=1,n,D=(A - x*A'+x*O(x^n));

%o A=1+x+x^2 + 3*x^3*A'/D + 2*x^4*(A')^2/D^2 + x^4*A^2*A''/D^3);polcoeff(A,n)}

%o for(n=0,30,print1(a(n),", "))

%Y Cf. A245313, A245310.

%K nonn

%O 0,4

%A _Paul D. Hanna_, Jul 19 2014

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