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A220897 Number of closed lambda-terms of size n with at most 3 free de Bruijn indices. 2
3, 13, 99, 962, 10732, 131715, 1741813, 24537945, 365779679, 5744911157, 94786034723, 1639198623818, 29658034018852, 560484305049943, 11046637024014049, 226728682400563206, 4839249231632997924, 107262821628220974029, 2465723931357450572707 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..18.

Katarzyna Grygiel and Pierre Lescanne, Counting and generating lambda-terms, arXiv preprint arXiv:1210.2610, 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, 3];

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

CROSSREFS

Sequence in context: A180709 A125207 A306082 * A267196 A268215 A323687

Adjacent sequences:  A220894 A220895 A220896 * A220898 A220899 A220900

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 31 2012

STATUS

approved

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Last modified September 24 15:33 EDT 2021. Contains 347643 sequences. (Running on oeis4.)