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 A172481 a(n) = (3*n*2^n+2^(n+4)+2*(-1)^n)/18. 6
 1, 2, 5, 11, 25, 55, 121, 263, 569, 1223, 2617, 5575, 11833, 25031, 52793, 111047, 233017, 487879, 1019449, 2126279, 4427321, 9204167, 19107385, 39612871, 82021945, 169636295, 350457401, 723284423, 1491308089, 3072094663, 6323146297, 13004206535, 26724240953 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The binomial transform is in A126184. An elephant sequence, see A175654 and A175655. There are 24 A vectors, with decimal values between 7 and 448, that lead for the corner squares to this sequence. Its companion sequence for the central square is A175656. Furthermore there are 36 A vectors, with decimal values between 15 and 480, that lead for the central square to four times this sequence for n >= -1. Its companion sequence for the corner squares is A059570. - Johannes W. Meijer, Aug 15 2010 a(n) is also the number of runs of weakly increasing parts in all compositions of n+1. a(2) = 5: (111), (12), (2)(1), (3). - Alois P. Heinz, Apr 30 2017 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,0,-4) FORMULA G.f.: (1-x-x^2)/((1+x)*(1-2*x)^2). a(n) = A001045(n-1)+2*a(n-1), n>0. a(n)+A139790(n) = 2^(n+1) = A000079(n+1). a(n) = A139790(n)+A140960(n). a(n) = A001045(n)+(-1)^n*A084219(n). a(n) = A127984(n) + 2^(n-1).  Application:  Problem 11623, AMM 119 (2012) 161. - Stephen J. Herschkorn, Feb 11 2012 MATHEMATICA Table[(3n 2^n+2^(n+4)+2(-1)^n)/18, {n, 0, 40}]  (* or *) CoefficientList[Series[(1-x-x^2)/((1+x)(1-2x)^2), {x, 0, 40}], x]  (* Harvey P. Dale, Mar 28 2011 *) PROG (MAGMA) [(3*n*2^n+2^(n+4)+2*(-1)^n)/18: n in [0..40]]; // Vincenzo Librandi, Aug 04 2011 (PARI) a(n)=(3*n*2^n+2^(n+4)+2*(-1)^n)/18 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A059570, A151529, A127984. Sequence in context: A291737 A177795 A092685 * A151529 A192922 A215091 Adjacent sequences:  A172478 A172479 A172480 * A172482 A172483 A172484 KEYWORD nonn,easy AUTHOR Paul Curtz, Feb 04 2010 EXTENSIONS Definition replaced by explicit formula by R. J. Mathar, Feb 11 2010 STATUS approved

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Last modified January 21 05:39 EST 2020. Contains 331104 sequences. (Running on oeis4.)