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A163434 Number of different fixed (possibly) disconnected tetrominoes bounded tightly by an n X n square. 4
0, 1, 70, 425, 1426, 3577, 7526, 14065, 24130, 38801, 59302, 87001, 123410, 170185, 229126, 302177, 391426, 499105, 627590, 779401, 957202, 1163801, 1402150, 1675345, 1986626, 2339377, 2737126, 3183545, 3682450, 4237801, 4853702 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

FORMULA

a(n) = (2n^2 -4n +1)*(3n^2 -6n +1), n>1.

G.f.: x^2*(1+65*x+85*x^2-9*x^3+2*x^4)/(1-x)^5. - Colin Barker, Apr 25 2012

E.g.f.: (6*x^4 + 12*x^3 - x^2 + x + 1)*exp(x) - 2 x - 1. - G. C. Greubel, Dec 23 2016

EXAMPLE

a(2)=1: the (connected) square tetromino.

MATHEMATICA

Join[{0}, Table[(2 n^2 - 4 n + 1)*(3 n^2 - 6 n + 1), {n, 2, 50}]] (* or *) Join[{0}, LinearRecurrence[{5, -10, 10, -5, 1}, {1, 70, 425, 1426, 3577}, 50]] (* G. C. Greubel, Dec 23 2016 *)

PROG

(PARI) concat([0], Vec(x^2*(1+65*x+85*x^2-9*x^3+2*x^4)/(1-x)^5 + O(x^50))) \\ G. C. Greubel, Dec 23 2016

CROSSREFS

Cf. A162674, A163433, A163435, A163437.

Sequence in context: A151556 A172222 A157369 * A154085 A220365 A007330

Adjacent sequences:  A163431 A163432 A163433 * A163435 A163436 A163437

KEYWORD

nonn,easy

AUTHOR

David Bevan, Jul 28 2009

STATUS

approved

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Last modified November 17 18:24 EST 2019. Contains 329241 sequences. (Running on oeis4.)