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URL: https://oeis.org/A383449

⇱ A383449 - OEIS

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A383449

Number of permutations of length n which avoid the patterns 123 and 4321.

0

1, 1, 2, 5, 13, 25, 25, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

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OFFSET

0,3

LINKS

Table of n, a(n) for n=0..110.

Permutation Pattern Avoidance Library (PermPAL), Av(123, 4321)

Index entries for linear recurrences with constant coefficients, signature (1).

FORMULA

G.f.: 25*x^6 + 25*x^5 + 13*x^4 + 5*x^3 + 2*x^2 + x + 1.

CROSSREFS

Sequence in context: A079780 A385699 A178621 * A362105 A309230 A048871

Adjacent sequences: A383446 A383447 A383448 * A383450 A383451 A383452

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, May 01 2025

EXTENSIONS

Offset corrected by Alois P. Heinz, Nov 07 2025

STATUS

approved