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 A158122 G.f. A(x) satisfies: A(x)^2 = 1/AGM(1, 1 - 8*x/A(x)^2 ). 5
 1, 2, 0, 0, 2, -4, 0, 0, -16, 40, 0, 0, 200, -544, 0, 0, -3006, 8540, 0, 0, 49956, -145720, 0, 0, -884352, 2625648, 0, 0, 16349648, -49161024, 0, 0, -311986480, 947069352, 0, 0, 6098614912, -18650752400, 0, 0, -121497078016, 373773754912, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS See A060691 for the expansion of AGM(1,1-8x), where AGM denotes the arithmetic-geometric mean. LINKS FORMULA G.f.: A(x) = sqrt( x/Series_Reversion( x/AGM(1,1-8*x) ) ). Self-convolution equals A158100. Contribution from Paul D. Hanna, Mar 14 2009: (Start) Quadrasections are A158212(n) = A158122(4n) and A158213 = A158122(4n+1); let B(x), C(x), be the g.f.s of A158212 and A158213, respectively, then C(x) = 2/B(x) so that A(x) = B(x^4) + x*C(x^4) = B(x^4) + 2*x/B(x^4) = 2/C(x^4) + x*C(x^4). (End) EXAMPLE G.f.: A(x) = 1 + 2*x + 2*x^4 - 4*x^5 - 16*x^8 + 40*x^9 + 200*x^12 -+... A(x)^2 = 1 + 4*x + 4*x^2 + 4*x^4 - 16*x^6 - 28*x^8 + 176*x^10 +... Contribution from Paul D. Hanna, Mar 14 2009: (Start) G.f. of quadrasection A158212 is: B(x) = 1 + 2*x - 16*x^2 + 200*x^3 - 3006*x^4 + 49956*x^5 +...; G.f. of quadrasection A158213 is C(x) = 2/B(x): C(x) = 2 - 4*x + 40*x^2 - 544*x^3 + 8540*x^4 - 145720*x^5 +... where g.f. A(x) = B(x^4) + x*C(x^4) = B(x^4) + 2*x/B(x^4). (End) PROG (PARI) {a(n)=polcoeff(sqrt(x/serreverse(x/agm(1, 1-8*x +x*O(x^n)))), n)} CROSSREFS Cf. A060691, A158100 (self-convolution), A258053. Cf. quadrasections: A158212, A158213. Sequence in context: A020474 A135589 A244312 * A028641 A325190 A141416 Adjacent sequences:  A158119 A158120 A158121 * A158123 A158124 A158125 KEYWORD sign AUTHOR Paul D. Hanna, Mar 13 2009 STATUS approved

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Last modified December 7 12:17 EST 2021. Contains 349581 sequences. (Running on oeis4.)