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A319436 Number of palindromic plane trees with n nodes. 5
1, 1, 2, 3, 6, 10, 20, 35, 68, 122, 234, 426, 808, 1484, 2798, 5167, 9700, 17974, 33656, 62498, 116826, 217236, 405646, 754938, 1408736, 2623188, 4892848, 9114036, 16995110, 31664136, 59034488, 110004243, 205068892, 382156686, 712363344, 1327600346, 2474618434 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

A rooted plane tree is palindromic if the sequence of branches directly under any given node is a palindrome.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..500

Gus Wiseman, The a(8) = 35 palindromic plane trees.

Gus Wiseman, The a(11) = 234 palindromic plane trees.

EXAMPLE

The a(7) = 20 palindromic plane trees:

  ((((((o))))))  (((((oo)))))  ((((ooo))))  (((oooo)))  ((ooooo))  (oooooo)

                 ((((o)(o))))  (((o(o)o)))  ((o(oo)o))  (o(ooo)o)

                 ((((o)(o))))  ((o((o))o))  (o((oo))o)  (oo(o)oo)

                 (((o))((o)))  (((o)o(o)))  ((oo)(oo))

                               (o(((o)))o)  ((o)oo(o))

                               ((o)(o)(o))  (o(o)(o)o)

MATHEMATICA

panplane[n_]:=If[n==1, {{}}, Join@@Table[Select[Tuples[panplane/@c], #==Reverse[#]&], {c, Join@@Permutations/@IntegerPartitions[n-1]}]];

Table[Length[panplane[n]], {n, 10}]

PROG

(PARI) PAL(p)={(1+p)/subst(1-p, x, x^2)}

seq(n)={my(p=O(1)); for(i=1, n, p=PAL(x*p)); Vec(p)} \\ Andrew Howroyd, Sep 19 2018

CROSSREFS

Cf. A000108, A000670, A001003, A005043, A008965, A025065, A032128, A118376, A242414, A317085, A317086, A317087, A319122, A319437.

Sequence in context: A030436 A030227 A180272 * A061551 A026034 A178381

Adjacent sequences:  A319433 A319434 A319435 * A319437 A319438 A319439

KEYWORD

nonn

AUTHOR

Gus Wiseman, Sep 18 2018

STATUS

approved

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Last modified November 17 11:02 EST 2019. Contains 329226 sequences. (Running on oeis4.)