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A131898
a(n) = 2^(n+1) + 2*n - 1.
3
1, 5, 11, 21, 39, 73, 139, 269, 527, 1041, 2067, 4117, 8215, 16409, 32795, 65565, 131103, 262177, 524323, 1048613, 2097191, 4194345, 8388651, 16777261, 33554479, 67108913, 134217779, 268435509, 536870967, 1073741881, 2147483707, 4294967357, 8589934655, 17179869249
OFFSET
0,2
COMMENTS
Row sums of triangle A131897.
Binomial transform of (1, 4, 2, 2, 2, ...).
a(n), n > 0, is the number of maximal subsemigroups of the Motzkin monoid of degree n + 1. - James Mitchell and Wilf A. Wilson, Jul 21 2017
LINKS
James East, Jitender Kumar, James D. Mitchell, and Wilf A. Wilson, Maximal subsemigroups of finite transformation and partition monoids, arXiv:1706.04967 [math.GR], 2017. [From James Mitchell and Wilf A. Wilson, Jul 21 2017]
FORMULA
G.f.: (-1-x+4*x^2)/((2*x-1)*(x-1)^2). - R. J. Mathar, Jul 03 2011
a(n) = 4*a(n-1) - 5*a(n-2) + 2*a(n-3). - Vincenzo Librandi, Jul 05 2012
E.g.f.: exp(x)*(2*(exp(x) + x) - 1). - Elmo R. Oliveira, Mar 08 2025
EXAMPLE
a(3) = 21 = sum of row 3 terms of triangle A131897: (11 + 4 + 2 + 4).
a(3) = 21 = (1, 3, 3, 1) dot (1, 4, 2, 2) = (1 + 12 + 6 + 2).
MATHEMATICA
CoefficientList[Series[(-1-x+4*x^2)/((2*x-1)*(x-1)^2), {x, 0, 40}], x] (* Vincenzo Librandi, Jul 05 2012 *)
PROG
(Magma) I:=[1, 5, 11]; [n le 3 select I[n] else 4*Self(n-1)-5*Self(n-2)+2*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Jul 05 2012
CROSSREFS
Cf. A131897.
Sequence in context: A163787 A166863 A163704 * A168642 A357750 A234597
KEYWORD
nonn,easy,changed
AUTHOR
Gary W. Adamson, Jul 25 2007
EXTENSIONS
New definition by R. J. Mathar, Jul 03 2011
STATUS
approved