A193037 G.f. A(x) satisfies: x = Sum_{n>=1} x^n*A(-x)^A022998(n), where A022998 is defined as "if n is odd then n else 2*n.".
1, 1, 3, 16, 99, 660, 4625, 33609, 251024, 1915365, 14866307, 117007587, 931682106, 7491746385, 60750081839, 496214311987, 4078991375519, 33718664525501, 280123674031062, 2337556609209193, 19584517345276853, 164677962557101656, 1389268739557153255
Offset: 0
Keywords
Examples
G.f.: A(x) = 1 + x + 3*x^2 + 16*x^3 + 99*x^4 + 660*x^5 + 4625*x^6 +... The g.f. satisfies: x = x*A(-x) + x^2*A(-x)^4 + x^3*A(-x)^3 + x^4*A(-x)^8 + x^5*A(-x)^5 + x^6*A(-x)^12 +...+ x^n*A(-x)^A022998(n) +... where A022998 begins: [1,4,3,8,5,12,7,16,9,20,11,24,13,28,15,32,...].
Programs
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Mathematica
CoefficientList[Series[Root[1 - #1 - x^2*#1^2 + (x - x^2)*#1^4 + x^2*#1^5 + (-x^3 + x^4)*#1^6 &, 1], {x, 0, 25}], x] (* Vaclav Kotesovec, Oct 18 2020 *) -
PARI
{a(n)=local(A=[1]);for(i=1,n,A=concat(A,0);A[#A]=polcoeff(sum(m=1,#A,(-x)^m*Ser(A)^((2-m%2)*m)),#A));if(n<0,0,A[n+1])} -
PARI
{a(n)=local(A=1+x);for(i=1,n,A=1+x*A^4-x^2*(A^2+A^4-A^5)-x^3*A^6+x^4*A^6+x*O(x^n));polcoeff(A,n)}
Formula
G.f. satisfies: 1 = A(x)/(1 - x^2*A(x)^2) - x*A(x)^4/(1 - x^2*A(x)^4).
G.f. satisfies: A(x) = 1 - x^2*A(x)^2 + x*(1-x)*A(x)^4 + x^2*A(x)^5 - x^3*(1-x)*A(x)^6.
a(n) ~ sqrt((s^4 - 3*r^2*s^6 + 4*r^3*s^6 + 2*r*s^2*(-1 - s^2 + s^3)) / (6*s^2 - 15*r^2*s^4 + 15*r^3*s^4 + r*(-1 - 6*s^2 + 10*s^3))) / (2 * sqrt(Pi) * n^(3/2) * r^n), where r = 0.1106746599331611304198664461476598606151090027202... and s = 1.30776993974681499155955325507126073446958968382... are real roots of the system of equations 1 + r^2*s^5 + (-1 + r)*r^3*s^6 = s + r^2*s^2 + (-1 + r)*r*s^4, r^2*s^4*(5 + 6*(-1 + r)*r*s) = 1 + 2*r^2*s + 4*(-1 + r)*r*s^3. - Vaclav Kotesovec, Oct 18 2020
Comments