2,2

Number of permutations of [n] with 2 sequences.

Number of 2 X n binary matrices that avoid simultaneously the right angled numbered polyomino patterns (ranpp) (00;1) and (11;0). An occurrence of a ranpp (xy;z) in a matrix A=(a(i,j)) is a triple (a(i1,j1), a(i1,j2), a(i2,j1)) where i1<i2, j1<j2 and these elements are in same relative order as those in the triple (x,y,z). - Sergey Kitaev (kitaev(AT)ms.uky.edu), Nov 11 2004

The number of edges in the dual Edwards-Venn digram graph with n-1 digits when n>2.

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 261.

I. Strazdins, Universal affine classification of Boolean functions, Acta Applic. Math. 46 (1997), 147-167.

A. W. F. Edwards, Cogwheels of the Mind, Johns Hopkins University Press, 2004, p. 82.

S. Kitaev, On multi-avoidance of right angled numbered polyomino patterns, Integers: Electronic Journal of Combinatorial Number Theory 4 (2004), A21, 20pp.

S. Kitaev, On multi-avoidance of right angled numbered polyomino patterns, University of Kentucky Research Reports (2004).

O.g.f.: 4x^3/((1-x)(1-2x)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 07 2008]

[seq (stirling2(n, 2)*4, n=1..30)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 06 2006

a=0; lst={}; k=4; Do[a+=k; AppendTo[lst, a]; k+=k, {n, 0, 5!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Dec 15 2008]

(PARI) a(n)=if(n<2, 0, 2^n-4)

(Other) sage: [gaussian_binomial(n, 1, 2)-3 for n in xrange(2, 32)] # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 31 2009]

Sequence in context: A011939 A028346 A079089 this_sequence A034508 A002932 A121312

Adjacent sequences: A028396 A028397 A028398 this_sequence A028400 A028401 A028402

nonn

N. J. A. Sloane (njas(AT)research.att.com).

Additional comments from Barbara Haas Margolius (margolius(AT)math.csuohio.edu) 2/12/01