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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A193641 Number of arrays of -1..1 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero. 9
 1, 3, 7, 15, 33, 73, 161, 355, 783, 1727, 3809, 8401, 18529, 40867, 90135, 198799, 438465, 967065, 2132929, 4704323, 10375711, 22884351, 50473025, 111321761, 245527873, 541528771, 1194379303, 2634286479, 5810101729, 12814582761 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Column 1 of A193648. Or yet empirical: row sums of triangle m/k | 0 1 2 3 4 5 6 7 ================================================== 0 | 1 1 | 1 2 2 | 1 2 4 3 | 1 2 4 8 4 | 1 4 4 8 16 5 | 1 4 12 8 16 32 6 | 1 4 12 32 16 32 64 7 | 1 6 12 32 80 32 64 128 which is triangle for numbers 2^k*C(m,k) with triplicated diagonals. - Vladimir Shevelev, Apr 13 2012 LINKS R. H. Hardin, Table of n, a(n) for n = 1..200 Tomislav Doslic and I. Zubac, Counting maximal matchings in linear polymers, Ars Mathematica Contemporanea 11 (2016) 255-276. FORMULA Empirical: a(n) = 2*a(n-1) + a(n-3). Empirical: G.f.: -x*(1+x+x^2) / ( -1+2*x+x^3 ); a(n) = A008998(n-3) + A008998(n-2) + A008998(n-1). - R. J. Mathar, Feb 19 2015 Empirical: a(n) = 1 + 2*A077852(n-2) for n >= 2. - Greg Dresden, Apr 04 2021 Empirical: partial sums of A052910. - Sean A. Irvine, Jul 14 2022 EXAMPLE Some solutions for n=6: 1 1 1 0 0 1 -1 1 0 -1 -1 0 0 0 -1 -1 -1 -1 -1 0 -1 -1 1 -1 1 1 1 1 1 0 1 1 -1 0 1 0 1 1 0 0 -1 -1 0 -1 -1 1 -1 1 1 1 1 0 1 0 -1 -1 1 1 0 0 -1 -1 -1 -1 0 -1 -1 -1 -1 0 1 1 -1 0 0 0 1 1 1 1 0 1 1 1 1 0 -1 0 0 0 0 0 0 -1 -1 -1 PROG (Haskell) a193641 n = a193641_list !! n a193641_list = drop 2 xs where xs = 1 : 1 : 1 : zipWith (+) xs (map (* 2) \$ drop 2 xs) -- Reinhard Zumkeller, Jan 01 2014 CROSSREFS Sequence in context: A269560 A146654 A363503 * A026701 A249512 A140498 Adjacent sequences: A193638 A193639 A193640 * A193642 A193643 A193644 KEYWORD nonn AUTHOR R. H. Hardin, Aug 02 2011 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 November 28 22:02 EST 2023. Contains 367420 sequences. (Running on oeis4.)