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A139086
G.f. satisfies: A(x) = 3*x - x^2 - 2*Series_Reversion( A(x) ).
1
1, 1, 4, 30, 316, 4116, 62296, 1058418, 19764860, 400070484, 8693577528, 201394483524, 4947738765928, 128383644586440, 3507060528884560, 100587324451979478, 3022202483800235964, 94935204982349494092
OFFSET
1,3
FORMULA
a(n) = 2*(-1)^n*A139085(n) for n>2 with a(1)=a(2)=1.
EXAMPLE
G.f.: A(x) = x + x^2 + 4*x^3 + 30*x^4 + 316*x^5 + 4116*x^6 +...
Series_Reversion(A(x)) = x - x^2 - 2*x^3 - 15*x^4 - 158*x^5 -...
which equals -G(-x) where G(x) = g.f. of A139085.
PROG
(PARI) {a(n)=local(A=x+x^2); if(n<1, 0, for(i=3, n+1, A=A+2*polcoeff(serreverse(A+x*O(x^i)), i)*x^i); polcoeff(A, n))}
CROSSREFS
Cf. A139085.
Sequence in context: A145348 A052574 A158834 * A243244 A293022 A360766
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 08 2008
STATUS
approved