The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A140789 We consider how many ways there are of coloring a square grid, n X n, using just two colors, black & white say. If the resulting grid has TWO lines of symmetry, then the number of different grids is given by this sequence. None of these counted are the images of any of the others under a rotation. If one wishes to count these as different, then each of these numbers can be multiplied by 2. 0
 0, 1, 8, 32, 448, 2240, 64512, 556032, 33521664, 553615360, 68717379584, 2233380896768, 562949684985856, 36310271727239168, 18446744004990074880, 2370406613402957905920, 2417851639194073977323520, 620178945462269582252179456, 1267650600228193372699684241408 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(2m) = 2^(m^2 - 1)*(2^m + 1) - 2^(m*(m + 1)/2). a(2m+1)= 2^(m^2 + 2*m + 1) - 2^((m^2 + 3*m + 2)/2). PROG (PARI) s=[0]; for(m=1, 15, s=concat(s, [2^(m^2-1)*(2^m+1)-2^(m*(m+1)/2), 2^(m^2+2*m+1)-2^((m^2+3*m+2)/2)])); s \\ Colin Barker, Mar 28 2014 CROSSREFS Cf. A140650. Sequence in context: A034193 A159277 A214539 * A120781 A288454 A139286 Adjacent sequences: A140786 A140787 A140788 * A140790 A140791 A140792 KEYWORD nonn AUTHOR Anthony C Robin, Jul 14 2008 EXTENSIONS More terms from Colin Barker, Mar 28 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 6 18:02 EST 2023. Contains 360111 sequences. (Running on oeis4.)