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A220895 Number of closed lambda-terms of size n with at most 1 free de Bruijn index. 3
1, 3, 13, 76, 542, 4493, 42131, 439031, 5020105, 62382279, 835980065, 12004984120, 183754242626, 2984264710781, 51220227153987, 925859588215096, 17571969962025822, 349210371834021295, 7249185099929421649, 156847124089924073770, 3530125495029323284404 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Katarzyna Grygiel and Pierre Lescanne, Counting and generating lambda-terms, arXiv preprint arXiv:1210.2610 [cs.LO], 2012.

FORMULA

Grygiel and Lescanne give a recurrence.

MATHEMATICA

T[0, m_] := m; T[n_, m_] := T[n, m] = T[n-1, m+1] + Sum[T[i, m] T[n-i-1, m], {i, 0, n-1}];

a[n_] := T[n, 1];

Table[a[n], {n, 0, 14}] (* Jean-Fran├žois Alcover, May 23 2017 *)

CROSSREFS

Sequence in context: A047730 A162435 A059040 * A336421 A189239 A074530

Adjacent sequences:  A220892 A220893 A220894 * A220896 A220897 A220898

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 31 2012

EXTENSIONS

More terms from Alois P. Heinz, May 23 2017

STATUS

approved

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Last modified October 26 14:28 EDT 2021. Contains 348267 sequences. (Running on oeis4.)