0,1

Number of tilings of a 4 X 4n+4 rectangle into T tetrominoes.

Numbers n such that 3^n = n/2 mod n. Cf. A0666013^n mod n. - Zak Seidov, Aug 26 2006

For n>=1, a(n) is equal to the number of functions f:{1,2...,n}->{1,2,3} such that for a fixed x in {1,2,...,n} and a fixed y in {1,2,3} we have f(x)<>y. - Aleksandar M. Janjic and Milan R. Janjic (agnus(AT)blic.net), Mar 27 2007

S. J. Cyvin and I. Gutman, Kekule structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see p. 203).

Franklin T. Adams-Watters, Table of n, a(n) for n = 0..200

Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Tanya Khovanova, Recursive Sequences

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 170

C. Moore, [math/9905012] Some Polyomino Tilings of the Plane

a(n) = 2*3^n; a(n) = 3a(n-1).

Pisot sequence E(x, y): a(0) = x, a(1) = y, a(n) = roundUp(a(n-1)^2/a(n-2)) = [ a(n-1)^2/a(n-2) + 1/2 ].

Pisot sequence L(x, y): a(0) = x, a(1) = y, a(n) = ceiling(a(n-1)^2/a(n-2)).

Pisot sequence P(x, y): a(0) = x, a(1) = y, a(n) = roundDown(a(n-1)^2/a(n-2)) = ceiling(a(n-1)^2/a(n-2) - 1/2).

Pisot sequence T(x, y): a(0) = x, a(1) = y, a(n) = floor(a(n-1)^2/a(n-2)) = [ a(n-1)^2/a(n-2) ].

G.f.: 2/(1-3x) . - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Oct 08 2007

Apart from initial term, same as A025192. Cf. A080643.

Adjacent sequences: A008773 A008774 A008775 this_sequence A008777 A008778 A008779

Sequence in context: A072852 A072853 A025192 this_sequence A134635 A114464 A062415

easy,nice,nonn

njas, David W. Wilson (davidwwilson(AT)comcast.net)