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A085583 Number of (3412,1234)-avoiding involutions in S_n. 0
1, 2, 4, 8, 16, 29, 51, 83, 131, 196, 286, 402, 554, 743, 981, 1269, 1621, 2038, 2536, 3116, 3796, 4577, 5479, 6503, 7671, 8984, 10466, 12118, 13966, 16011, 18281, 20777, 23529, 26538, 29836, 33424, 37336, 41573, 46171, 51131, 56491, 62252, 68454, 75098 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..44.

E. S. Egge, Restricted 3412-Avoiding Involutions: Continued Fractions, Chebyshev Polynomials and Enumerations, sec. 8

Index entries for linear recurrences with constant coefficients, signature (3,-1,-5,5,1,-3,1).

FORMULA

a(n) = (2*n^4-4*n^3+28*n^2-2*n+81-6*n*(-1)^n+15*(-1)^n)/96.

G.f.: -x*(x^6-2*x^5+x^4+3*x^3-x^2-x+1) / ((x-1)^5*(x+1)^2). - Colin Barker, Jul 16 2013

CROSSREFS

Sequence in context: A177269 A018726 A049884 * A160786 A054154 A292793

Adjacent sequences:  A085580 A085581 A085582 * A085584 A085585 A085586

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Jul 06 2003

EXTENSIONS

More terms from Colin Barker, Jul 16 2013

STATUS

approved

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Last modified April 23 13:25 EDT 2019. Contains 322386 sequences. (Running on oeis4.)