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 A290604 a(0) = 2, a(1) = 2; for n > 1, a(n) = a(n-1) + 2*a(n-2) + 3. 2
 2, 2, 9, 16, 37, 72, 149, 296, 597, 1192, 2389, 4776, 9557, 19112, 38229, 76456, 152917, 305832, 611669, 1223336, 2446677, 4893352, 9786709, 19573416, 39146837, 78293672, 156587349, 313174696, 626349397, 1252698792, 2505397589, 5010795176, 10021590357 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Ratio of successive terms approaches 2. LINKS Iain Fox, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2,1,-2) FORMULA a(n) = (2^(n+2) + 2*(-1)^n)/3 + 2^n - (3-(-1)^n)/2. a(n) = A014113(n+1) + A141023(n). G.f.: (2 - 2*x + 3*x^2)/(1 - 2*x - x^2 + 2*x^3). a(n) = 2*a(n-1) + a(n-2) - 2*a(n-3), n > 2. - Iain Fox, Dec 18 2017 EXAMPLE a(0) = 2. a(1) = 2. a(2) = 2 + 2*2 + 3 = 9. a(3) = 9 + 2*2 + 3 = 16. a(4) = 16 + 9*2 + 3 = 37. ... MATHEMATICA Table[(2^(n + 2) + 2 (-1)^n) / 3 + 2^n - (3 - (-1)^n) / 2, {n, 0, 40}] (* Vincenzo Librandi, Oct 20 2017 *) PROG (PARI) Vec((2/(1-x-2*x^2)) + (3*x^2/((1-x)*(1-x-2*x^2))) + O(x^50)) \\ Michel Marcus, Oct 12 2017 (PARI) first(n) = Vec((2 - 2*x + 3*x^2)/(1 - 2*x - x^2 + 2*x^3) + O(x^n)) \\ Iain Fox, Dec 18 2017 (MAGMA) [(2^(n+2)+2*(-1)^n)/3+2^n-(3-(-1)^n)/2: n in [0..40]]; // Vincenzo Librandi, Oct 20 2017 CROSSREFS Sequence in context: A185755 A278458 A309705 * A039796 A224244 A007024 Adjacent sequences:  A290601 A290602 A290603 * A290605 A290606 A290607 KEYWORD easy,nonn AUTHOR Iain Fox, Oct 11 2017 STATUS approved

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Last modified December 5 12:24 EST 2021. Contains 349557 sequences. (Running on oeis4.)