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Search: id:A089408
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| 1, 1, 2, 1, 2, 2, 4, 5, 10, 14, 28, 42, 84, 132, 264, 429, 858, 1430, 2860, 4862, 9724, 16796, 33592, 58786, 117572, 208012, 416024, 742900, 1485800, 2674440, 5348880, 9694845, 19389690, 35357670, 70715340, 129644790, 259289580, 477638700
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OFFSET
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0,3
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COMMENT
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The number of n-node binary trees fixed by the corresponding automorphism(s). Essentially A000108 interleaved with A068875.
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LINKS
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A. Karttunen, C-program for computing the initial terms of this sequence
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FORMULA
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a(0)=1, a(2n) = 2*A000108(n-1), a(2n+1) = A000108(n)
G.f.: (1+4x-(1+2x)sqrt(1-4x^2))/(2x) - Paul Barry (pbarry(AT)wit.ie), Apr 11 2005
C(2*j,j)/(1+j)*i, i=1..2),j>=0. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 29 2007
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MAPLE
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seq(seq(binomial(2*j, j)/(1+j)*i, i=1..2), j=0..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 29 2007
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PROGRAM
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(Scheme) (define (A089408 n) (cond ((zero? n) 1) ((even? n) (* 2 (A000108 (-1+ (/ n 2))))) (else (A000108 (/ (-1+ n) 2)))))
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CROSSREFS
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Cf. A089402.
Cf. A000108.
Sequence in context: A163373 A117193 A026832 this_sequence A079318 A050315 A128978
Adjacent sequences: A089405 A089406 A089407 this_sequence A089409 A089410 A089411
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KEYWORD
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nonn,easy
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AUTHOR
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Antti Karttunen (His_Firstname.His_Surname(AT)gmail.com), Nov 29 2003
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