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 A088218 Total number of leaves in all rooted ordered trees with n edges. 80
 1, 1, 3, 10, 35, 126, 462, 1716, 6435, 24310, 92378, 352716, 1352078, 5200300, 20058300, 77558760, 300540195, 1166803110, 4537567650, 17672631900, 68923264410, 269128937220, 1052049481860, 4116715363800, 16123801841550, 63205303218876, 247959266474052 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Essentially the same as A001700, which has more information. Note that the unique rooted tree with no edges has no leaves, so a(0)=1 is by convention. - Michael Somos, Jul 30 2011 Number of ordered partitions of n into n parts, allowing zeros (cf. A097070) is binomial(2*n-1,n) = a(n) = essentially A001700. - Vladeta Jovovic, Sep 15 2004 Hankel transform is A000027; example: Det([1,1,3,10;1,3,10,35;3,10,35,126; 10,35,126,462]) = 4. - Philippe Deléham, Apr 13 2007 a(n) is the number of functions f:[n]->[n] such that for all x,y in [n] if x=1, B. Dubalski (dubalski(AT)atr.bydgoszcz.pl), Feb 05 2002 (in A060150) a(n) = (0^n + C(2n, n))/2. - Paul Barry, May 21 2004 a(n) is the coefficient of x^n in 1 / (1 - x)^n and also the sum of the first n coefficients of 1 / (1 - x)^n. Given B(x) with the property that the coefficient of x^n in B(x)^n equals the sum of the first n coefficients of B(x)^n, then B(x) = B(0) / (1 - x). G.f.: 1 / (2 - C(x)) = (1 - x*C(x))/sqrt(1-4*x) where C(x) is g.f. for Catalan numbers A000108. Second equation added by Wolfdieter Lang, Nov 22 2012. G.f.: (1 + 1 / sqrt(1 - 4*x)) / 2. a(n) = binomial( 2*n - 1, n). From Paul Barry, Nov 02 2004: (Start) a(n) = Sum_{k=0..n} binomial(2n, k)cos((n-k)*Pi)}; a(n) = Sum_{k=0..n} binomial(n, (n-k)/2)(1+(-1)^(n-k))cos(k*Pi/2)/2} (with interpolated zeros); a(n) = Sum_{k=0..floor(n/2)} binomial(n, k)cos((n-2k)Pi/2)} (with interpolated zeros); (End) a(n) = A110556(n)*(-1)^n, central terms in triangle A110555. - Reinhard Zumkeller, Jul 27 2005 a(n) = Sum_{0<=k<=n} A094527(n,k)*(-1)^k. - Philippe Deléham, Mar 14 2007 From Paul Barry, Mar 29 2010: (Start) G.f.: 1/(1-x/(1-2x/(1-(1/2)x/(1-(3/2)x/(1-(2/3)x/(1-(4/3)x/(1-(3/4)x/(1-(5/4)x/(1-... (continued fraction); E.g.f.: (of aerated sequence) (1 + Bessel_I(0, 2*x))/2. (End) a(n + 1) = A001700(n). a(n) = A024718(n) - A024718(n - 1). E.g.f.: E(x) = 1+x/(G(0)-2*x) ; G(k) = (k+1)^2+2*x*(2*k+1)-2*x*(2*k+3)*((k+1)^2)/G(k+1); (continued fraction). - Sergei N. Gladkovskii, Dec 21 2011 a(n) = Sum_{k=0..n}(-1)^k*binomial(2*n,n+k). - Mircea Merca, Jan 28 2012 a(n) = rf(n,n)/ff(n,n), where rf is the rising factorial and ff the falling factorial. - Peter Luschny, Nov 21 2012 D-finite with recurrence: n*a(n) +2*(-2*n+1)*a(n-1) = 0. - R. J. Mathar, Dec 04 2012 a(n) = binomial(2*n-1, n). - Vincenzo Librandi, Aug 07 2014 a(n) = hypergeom([1-n,-n],,1). - Peter Luschny, Sep 22 2014 G.f.: 1 + x/W(0), where W(k) = 4*k+1 - (4*k+3)*x/(1 - (4*k+1)*x/(4*k+3 - (4*k+5)*x/(1 - (4*k+3)*x/W(k+1)  ))) ; (continued fraction). - Sergei N. Gladkovskii, Nov 13 2014 EXAMPLE G.f. = 1 + x + 3*x^2 + 10*x^3 + 35*x^4 + 126*x^5 + 462*x^6 + 1716*x^7 + ... The five rooted ordered trees with 3 edges have 10 leaves. ..x........................ ..o..x.x..x......x......... ..o...o...o.x..x.o..x.x.x.. ..r...r....r....r.....r.... MAPLE seq(binomial(2*n-1, n), n=0..24); # Peter Luschny, Sep 22 2014 MATHEMATICA a[ n_] := SeriesCoefficient[(1 - x)^-n, {x, 0, n}]; c = (1 - (1 - 4 x)^(1/2))/(2 x); CoefficientList[Series[1/(1-(c-1)), {x, 0, 20}], x] (* Geoffrey Critzer, Dec 02 2010 *) Table[Binomial[2 n - 1, n], {n, 0, 20}] (* Vincenzo Librandi, Aug 07 2014 *) a[ n_] := If[ n < 0, 0, With[ {m = 2 n}, m! SeriesCoefficient[ (1 + BesselI[0, 2 x]) / 2, {x, 0, m}]]]; (* Michael Somos, Nov 22 2014 *) PROG (PARI) {a(n) = sum( i=0, n, binomial(n+i-2, i))}; (PARI) {a(n) = if( n<0, 0, polcoeff( (1 + 1 / sqrt(1 - 4*x + x * O(x^n))) / 2, n))}; (PARI) {a(n) = if( n<0, 0, polcoeff( 1 / (1 - x + x * O(x^n))^n, n))}; (PARI) {a(n) = if( n<0, 0, binomial( 2*n - 1, n))}; (PARI) {a(n) = if( n<1, n==0, polcoeff( subst((1 - x) / (1 - 2*x), x, serreverse( x - x^2 + x * O(x^n))), n))}; (Sage) def A088218(n):     return rising_factorial(n, n)/falling_factorial(n, n) [A088218(n) for n in (0..24)]  # Peter Luschny, Nov 21 2012 (MAGMA) [Binomial(2*n-1, n): n in [0..30]]; // Vincenzo Librandi, Aug 07 2014 CROSSREFS Cf. A001700, A024718, A110556. Main diagonal of A071919 and of A305161. Sequence in context: A318117 A110556 A001700 * A300975 A072266 A085282 Adjacent sequences:  A088215 A088216 A088217 * A088219 A088220 A088221 KEYWORD nonn AUTHOR Michael Somos, Sep 24 2003 STATUS approved

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Last modified November 28 21:56 EST 2020. Contains 338755 sequences. (Running on oeis4.)