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 A087223 G.f. satisfies A(x) = f(x) + x*A(x)*f(x)^3, where f(x)=sum(k>=0,x^((4^n-1)/3)). 1
 1, 2, 5, 14, 36, 96, 254, 676, 1792, 4756, 12621, 33490, 88868, 235818, 625764, 1660510, 4406296, 11692452, 31026836, 82332140, 218474784, 579739960, 1538385398, 4082226194, 10832507040, 28744906148, 76276860598, 202406625820 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA a(n) = A087221(3n+1). EXAMPLE Given f(x) = 1 +x +x^5 +x^21 +x^85 +x^341 +... so that f(x)^3 = 1 +3x +3x^2 +x^3 +3x^5 +6x^6 +3x^7 +3x^10 +... then A(x) = (1+x+x^5+...) + x*A(x)*(1+3x+3x^2+x^3+3x^5+6x^6 +...) = 1 +2x +5x^2 +14x^3 +36x^4 +96x^5 +254x^6 +... PROG (PARI) a(n)=local(A, m); if(n<1, n==0, m=1; A=1+O(x); while(m<=3*n+3, m*=4; A=1/(1/subst(A, x, x^4)-x)); polcoeff(A, 3*n+1)) CROSSREFS Cf. A087221, A087222, A087224. Sequence in context: A201371 A182890 A102714 * A005955 A186903 A062197 Adjacent sequences:  A087220 A087221 A087222 * A087224 A087225 A087226 KEYWORD nonn AUTHOR Paul D. Hanna, Aug 27 2003 STATUS approved

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