login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A158120 Unsigned bisection of A157304 and A157305. 2
1, 2, 26, 1378, 141202, 22716418, 5218302090, 1619288968386, 653379470919714, 333014944014777730, 209463165121436380282, 159492000935562428176162, 144654795258284936534929586, 154140229756873813307283828098 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Paul D. Hanna, Table of n, a(n) for n=0..50

EXAMPLE

G.f.: A(x) = 1 + 2*x + 26*x^2 + 1378*x^3 + 141202*x^4 +...

RELATED FUNCTIONS.

G.f. of A157305, B(x) = x + A(-x^2), satisfies the condition

that both B(x) and F(x) = B(x*F(x)^2) = o.g.f. of A157307

have zeros for every other coefficient after initial terms:

A157305 = [1,1,-2,0,26,0,-1378,0,141202,0,-22716418,0,...];

A157307 = [1,1,0,-7,0,242,0,-17771,0,2189294,0,-404590470,0,...].

...

G.f. of A157304, C(x) = 2+x - A(-x^2), satisfies the condition

that both C(x) and G(x) = C(x/G(x)^2) = o.g.f. of A157302

have zeros for every other coefficient after initial terms:

A157308 = [1,1,2,0,-26,0,1378,0,-141202,0,22716418,0,...];

A157302 = [1,1,0,-5,0,183,0,-14352,0,1857199,0,-355082433,0,...].

...

PROG

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

CROSSREFS

Cf. A157304, A157305, A157302, A157307, A158119.

Sequence in context: A173103 A002704 A015215 * A209916 A337578 A156213

Adjacent sequences:  A158117 A158118 A158119 * A158121 A158122 A158123

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Mar 12 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 18 14:45 EDT 2020. Contains 337169 sequences. (Running on oeis4.)