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 A050147 a(n) = T(n,n-1), array T as in A050143. Also T(2n+1,n), array T as in A055807. 2
 1, 3, 12, 56, 280, 1452, 7700, 41456, 225648, 1238420, 6840988, 37986984, 211842696, 1185635388, 6655993380, 37463920608, 211350457824, 1194706644516, 6765300359468, 38370431711000, 217931108199672 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA G.f.: x*((-x^2 + 4*x + 1)/(2*sqrt(x^2 - 6*x + 1)) -x/2 + 1/2). - Vladimir Kruchinin, Nov 25 2014 a(n) = C(2*n-3,n-2) + Sum(i=0..n-2} C(n,i+1)*C(n+i-2,n-2). - Vladimir Kruchinin, Nov 25 2014 a(n) ~ (1 + sqrt(2))^(2*n-2) / (2^(1/4) * sqrt(Pi*n)). - Vaclav Kotesovec, Feb 14 2021 PROG (Maxima) a(n):=if n=1 then 1 else sum((binomial(n, i+1))*binomial(n+i-2, n-2), i, 0, n-2)+binomial(2*n-3, n-2); /* Vladimir Kruchinin, Nov 25 2014 */ CROSSREFS Cf. A002003, A006318, A050143, A055807. Sequence in context: A284843 A107318 A176281 * A259800 A120921 A226316 Adjacent sequences:  A050144 A050145 A050146 * A050148 A050149 A050150 KEYWORD nonn AUTHOR STATUS approved

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Last modified September 20 23:04 EDT 2021. Contains 347596 sequences. (Running on oeis4.)