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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A181237 Number of (3n) X 3 binary matrices with all row sums equal and all column sums equal. 1
 14, 182, 3362, 69302, 1513514, 34306274, 798145922, 18931023542, 455746863002, 11101993582682, 273053990926082, 6769463525042402, 168956196145732802, 4241145331821456002, 106989959570749263362, 2710690928812030164662 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Row 3 of A181236. LINKS Robert Israel, Table of n, a(n) for n = 1..630 (first 112 terms from R. H. Hardin) FORMULA From Robert Israel, Oct 30 2014: (Start) a(n) = 2 * (1 + (3*n)!/(n!)^3). a(n+1) = (3*(3*n+2)*(3*n+1)*a(n) - 52*n^2 - 50*n - 10)/(n+1)^2. (End) EXAMPLE All solutions for 3 X 3: ..0..0..0....0..0..1....0..0..1....0..1..0....0..1..0....0..1..1....0..1..1 ..0..0..0....0..1..0....1..0..0....0..0..1....1..0..0....1..0..1....1..1..0 ..0..0..0....1..0..0....0..1..0....1..0..0....0..0..1....1..1..0....1..0..1 ... ..1..0..0....1..0..0....1..0..1....1..0..1....1..1..0....1..1..0....1..1..1 ..0..0..1....0..1..0....0..1..1....1..1..0....0..1..1....1..0..1....1..1..1 ..0..1..0....0..0..1....1..1..0....0..1..1....1..0..1....0..1..1....1..1..1 MAPLE seq(2 * (1 + (3*n)!/(n!)^3), n = 1 .. 20); # Robert Israel, Oct 30 2014 MATHEMATICA Table[2 (1 + (3 n)! / (n!)^3), {n, 20}] (* Vincenzo Librandi, Oct 30 2014 *) PROG (Magma) [2*(1+Factorial(3*n)/Factorial(n)^3): n in [1..20]]; // Vincenzo Librandi, Oct 30 2014 CROSSREFS Cf. A181236. Sequence in context: A170695 A170733 A186229 * A091030 A179090 A165152 Adjacent sequences: A181234 A181235 A181236 * A181238 A181239 A181240 KEYWORD nonn AUTHOR R. H. Hardin, Oct 10 2010 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 September 30 07:44 EDT 2023. Contains 365781 sequences. (Running on oeis4.)