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 A061981 a(n) = 3^n - 2*n - 1. 5
 0, 0, 4, 20, 72, 232, 716, 2172, 6544, 19664, 59028, 177124, 531416, 1594296, 4782940, 14348876, 43046688, 129140128, 387420452, 1162261428, 3486784360, 10460353160, 31381059564, 94143178780, 282429536432, 847288609392 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Harry J. Smith, Table of n, a(n) for n = 0..200 Brandon Alberts and Jack Klys, The distribution of H8-extensions of quadratic fields, arXiv:1611.05595 [math.NT], 2016. See p. 17. Index entries for linear recurrences with constant coefficients, signature (5,-7,3). FORMULA From Bruno Berselli, Jan 31 2012: (Start) G.f.: 4*x^2/((1-3*x)*(1-x)^2). a(n) = A186948(n) - 1. a(n+2) = 4*A000340(n). (End) From Deisy J. Camacho, Feb 26 2021 (Start) a(n) = Sum_{j=2..n} Sum_{i=0..j} n!/((j-i)!*i!*(n-j)!). a(n) = 4 + 4*a(n-1) - 3*a(n-2). (End) E.g.f.: exp(3*x) - (2*x + 1)*exp(x). - G. C. Greubel, Jun 13 2022 MATHEMATICA Table[3^n-2n-1, {n, 0, 30}] (* or *) LinearRecurrence[{5, -7, 3}, {0, 0, 4}, 30] (* Harvey P. Dale, Mar 30 2018 *) PROG (PARI) { for (n=0, 200, write("b061981.txt", n, " ", 3^n - 2*n - 1) ) } \\ Harry J. Smith, Jul 29 2009 (SageMath) [3^n -(2*n+1) for n in (0..40)] # G. C. Greubel, Jun 13 2022 CROSSREFS Column of A061980. Cf. A000340, A186948. Sequence in context: A291526 A303011 A197426 * A054611 A329174 A057333 Adjacent sequences: A061978 A061979 A061980 * A061982 A061983 A061984 KEYWORD nonn,easy AUTHOR Henry Bottomley, May 24 2001 STATUS approved

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Last modified June 8 04:57 EDT 2023. Contains 363157 sequences. (Running on oeis4.)