A179200 E.g.f. equals the real part of the i-th iteration of (x + x^2), where i=sqrt(-1).

0, 1, 0, -6, 60, -600, 5880, -38640, -624960, 45077760, -1773129600, 58531809600, -1657462435200, 33703750080000, 171919752076800, -76383384045696000, 6034124486347776000, -348318907415331840000, 15862493882862941184000

Offset: 0

Author

Paul D. Hanna, Jul 02 2010

Keywords

• sign

Comments

Let H(x) equal the i-th iteration of (x + x^2), then

. the inverse of H(x) equals the conjugate of H(x);

. H(x+x^2) = H(x) + H(x)^2;

. H(x) = F(x) + i*G(x) where G(x) = e.g.f. of A179201 and F(x) = e.g.f. of this sequence, where H(F(x) - i*G(x)) = x;

. coefficients of H(x) form the first column of triangular matrix A030528 raised to the i-th power, where A030528(n,k) = C(k,n-k).

Examples

			E.g.f: F(x) = x - 6*x^3/3! + 60*x^4/4! - 600*x^5/5! + 5880*x^6/6! +...
The e.g.f. of A179201, G(x), begins:
G(x) = 2*x^2/2! - 6*x^3/3! + 12*x^4/4! + 200*x^5/5! - 6240*x^6/6! + 139440*x^7/7! - 2869440*x^8/8! +...
The i-th iteration of (x + x^2) = H(x) = F(x) + i*G(x), begins:
H(x) = x + i*x^2 - (1 + i)*x^3 + (5 + i)*x^4/2 - (15 - 5*i)*x^5/3 + (49 - 52*i)*x^6/6 - (23 - 83*i)*x^7/3 - (93 + 427*i)*x^8/6 + (15652 + 18537*i)*x^9/126 - (61567 + 24585*i)*x^10/126 + (369519 - 42094*i)*x^11/252 - (1743963 - 1222750*i)*x^12/504 + ...
where H(F(x) - i*G(x)) = x.
		

Crossrefs

Cf. A179201, A030528.

Programs

PARI

{a(n)=local(M=matrix(n+1,n+1,r,c,if(r>=c,binomial(c,r-c))),L=sum(k=1,#M,-(M^0-M)^k/k),N=sum(k=0,#L,(I*L)^k/k!));if(n<1,0,real(n!*N[n,1]))}

Formula

E.g.f.: F(x) satisfies:

. F(x) = (G(x+x^2)/G(x) - 1)/2

. G(x) = sqrt( F(x) + F(x)^2 - F(x+x^2) )

where G(x) is the e.g.f. of A179201.