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A001699 Number of binary trees of height n; or products (ways to insert parentheses) of height n when multiplication is non-commutative and non-associative.
(Formerly M3087 N1251)
16
1, 1, 3, 21, 651, 457653, 210065930571, 44127887745696109598901, 1947270476915296449559659317606103024276803403, 3791862310265926082868235028027893277370233150300118107846437701158064808916492244872560821 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Approaches 1.5028368...^(2^n). Row sums of A065329 as square array. - Henry Bottomley, Oct 29 2001. Also row sum of square array A073345 (AK).

REFERENCES

I. M. H. Etherington, On non-associative combinations, Proc. Royal Soc. Edinburgh, 59 (Part 2, 1938-39), 153-162.

T. K. Moon, Enumerations of binary trees, types of trees and the number of reversible variable length codes, submitted to Discrete Applied Mathematics, 2000.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

LINKS

David Wasserman, Table of n, a(n) for n = 0..12 [Shortened file because terms grow rapidly: see Wasserman link below for an additional term]

A. V. Aho and N. J. A. Sloane, Some doubly exponential sequences, Fib. Quart., 11 (1973), 429-437.

H. Bottomley, Illustration of initial terms

C. Lenormand, Arbres et permutations II, see p. 6

David Wasserman, Table of n, a(n) for n = 0..13

Eric Weisstein's World of Mathematics, Binary Tree

Index entries for "core" sequences

Index entries for sequences related to rooted trees

Index entries for sequences related to trees

Index entries for sequences related to parenthesizing

Index entries for sequences of form a(n+1)=a(n)^2 + ...

FORMULA

a(n+1) = 2*a(n)*(a(0)+...+a(n-1))+a(n)^2.

a(n+1) = a(n)^2+a(n)+a(n)*sqrt(4*a(n)-3), if n>0.

a(n) = A003095(n+1) - A003095(n) = A003095(n)^2 - A003095(n) + 1. - Henry Bottomley, Apr 26 2001; offset of LHS corrected by Anindya Bhattacharyya, Jun 21 2013

a(n) = A059826(A003095(n-1)).

MAPLE

s := proc(n) local i, j, ans; ans := [ 1 ]; for i to n do ans := [ op(ans), 2*(add(j, j=ans)-ans[ i ])*ans[ i ]+ans[ i ]^2 ] od; RETURN(ans); end; s(10);

MATHEMATICA

a[0] = 1; a[n_] := a[n] = 2*a[n-1]*Sum[a[k], {k, 0, n-2}] + a[n-1]^2; Table[a[n], {n, 0, 9}] (* Jean-Fran├žois Alcover, May 16 2012 *)

PROG

(PARI) {a(n) = if( n<=1, n>= 0, a(n-1) * (a(n-1) + a(n-2) + a(n-1) / a(n-2)))} /* Michael Somos, 2000 */

CROSSREFS

Cf. A002658, A056207, A002449, A003095.

Cf. A004019.

Sequence in context: A093549 A012044 A098918 * A171104 A057600 A162924

Adjacent sequences:  A001696 A001697 A001698 * A001700 A001701 A001702

KEYWORD

nonn,easy,core,nice

AUTHOR

N. J. A. Sloane, Jeffrey Shallit

STATUS

approved

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Last modified September 3 01:21 EDT 2014. Contains 246369 sequences.