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 A138175 Row sums of the Riordan array (1/(1+x),x(1+2x)/(1+x)^3)^(-1). 1
 1, 2, 4, 10, 24, 62, 156, 408, 1048, 2758, 7164, 18922, 49488, 131016, 344208, 912720, 2405496, 6385814, 16868604, 44818494, 118595064, 315299694, 835423164, 2222185344, 5894038944, 15684059112 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A transform of 2^n by the Riordan array (1,x(1-x^2))^(-1). (1/(1+x),x(1+2x)/(1+x)^3)^(-1) factors as (1,x(1-x^2))^(-1)*(1/(1-x),x/(1-x)). Hankel transform is A138176. LINKS FORMULA G.f.: 1/(1-2v) where v=(2/sqrt(3))*sin(asin(x*3*sqrt(3)/2)/3), the reversion of x(1-x^2); Conjecture: 12*n*(n-1)*(39*n-88)*a(n) -8*(n-1)*(156*n^2-352*n+27)*a(n-1) +9*(-351*n^3-2196*n^2-4325*n+2680)*a(n-2) +24*(39*n-49)*(3*n-7)*(3*n-8)*a(n-3)=0.- R. J. Mathar, Oct 25 2012 CROSSREFS Sequence in context: A230551 A246566 A230553 * A121691 A124499 A303840 Adjacent sequences:  A138172 A138173 A138174 * A138176 A138177 A138178 KEYWORD easy,nonn AUTHOR Paul Barry, Mar 03 2008 STATUS approved

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Last modified July 28 17:15 EDT 2021. Contains 346335 sequences. (Running on oeis4.)