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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A157306 G.f. A(x) satisfies the condition that both G(x) = A(x/G(x)) and H(x) = A(x*H(x)) have zeros for every other coefficient after initial terms; g.f. of dual sequence A157303 satisfies the same condition. 5
 1, 1, -1, -5, 23, 151, -1249, -10961, 122975, 1380703, -18981121, -261461441, 4220277887, 69016559743, -1278668869633, -24212706029825, 507099112447487, 10908810091109887, -255195984676134913, -6145413122840501249 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS FORMULA For n>=1, [x^(2n)] A(x)^(2n+1) = 0. For n>=1, [x^(2n+1)] 1/A(x)^(2n) = 0. G.f. satisfies: A(x) = G(x*A(x)) where G(x) = A(x/G(x)) = x/Series_Reversion(x*A(x)) = g.f. of A157305. G.f. satisfies: A(x) = H(x/A(x)) where H(x) = A(x*H(x)) = Series_Reversion(x/A(x))/x = g.f. of A157307. EXAMPLE G.f.: A(x) = 1 + x - x^2 - 5*x^3 + 23*x^4 + 151*x^5 - 1249*x^6 -++-... ... Let G(x) = A(x/G(x)) so that A(x) = G(x*A(x)) then G(x) = 1 + x - 2*x^2 + 26*x^4 - 1378*x^6 + 141202*x^8 -+... has alternating zeros in the coefficients (cf. A157305): [1,1,-2,0,26,0,-1378,0,141202,0,-22716418,0,5218302090,0,...] ... Let H(x) = A(x*H(x)) so that A(x) = H(x/A(x)) then H(x) = 1 + x - 7*x^3 + 242*x^5 - 17771*x^7 + 2189294*x^9 -+... has alternating zeros in the coefficients (cf. A157307): [1,1,0,-7,0,242,0,-17771,0,2189294,0,-404590470,0,104785114020,0,...] ... ZERO COEFFICIENTS IN POWERS OF G.F. A(x). Odd powers A(x)^(2n+1) yield zeros at even positions 2n for n>=1: A^3: [1,3, 0, -20,39,609,-2806,-41598,302361,4976719,...]; A^5: [1,5,5,-35, 0, 1176,-2530,-80630,359635,9462895,...]; A^7: [1,7,14,-42,-98,1694, 0, -122408,263963,14465941,...]; A^9: [1,9,27,-33,-243,1989,4797,-159939, 0, 19515184,...]; ... Even negative powers 1/A(x)^(2n) yield zeros at odd positions 2n+1 for n>=1: A^-2: [1,-2,5, 0, -56,-112,2916,12112,-284944,-1831680,...]; A^-4: [1,-4,14,-20,-87, 0, 5720,11440,-586040,-2389920,...]; A^-6: [1,-6,27,-68,-33,186,7865, 0, -865776,-1731552,...]; A^-8: [1,-8,44,-152,182,136,9404,-19400,-1095871, 0, ...]; ... PROG (PARI) {a(n)=local(A=[1, 1]); for(i=1, 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^2/serreverse(x*Ser(A)))[ #A], t, 0))); A[n+1]} CROSSREFS Cf. A157305, A157307, A157302, A157303 (dual), A157304. Sequence in context: A128884 A007836 A233568 * A306185 A336183 A342196 Adjacent sequences:  A157303 A157304 A157305 * A157307 A157308 A157309 KEYWORD sign AUTHOR Paul D. Hanna, Feb 28 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.

Last modified September 23 14:40 EDT 2021. Contains 347618 sequences. (Running on oeis4.)