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 A238539 A fourth-order linear divisibility sequence: a(n) := (1/9)*(2^n + (-1)^n)*(2^(3*n) - (-1)^n). 4
 1, 35, 399, 7735, 112871, 1893255, 29593159, 479082695, 7620584391, 122287263175, 1953732901319, 31282632909255, 500338874618311, 8006888009380295, 128098480026087879, 2049669505409577415, 32793961486615474631, 524709388585350492615, 8395302178969583120839 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This is a divisibility sequence, that is, if n | m then a(n) | a(m). This is a consequence of the following more general result: The polynomials P(n,x,y) := (x^n + y^n)*(x^(3*n) - y^(3*n)) form a divisibility sequence in the polynomial ring Z[x,y]. See the Bala link. The sequence satisfies a homogeneous linear recurrence of the fourth order. However, it does not belong to the family of linear divisibility sequences of the fourth order studied by Williams and Guy, which have o.g.f.s of the form x*(1 - q*x^2)/Q(x), Q(x) a quartic polynomial and q an integer. For sequences of a similar type see A238536 through A238541. LINKS Wikipedia, Divisibility sequence" H. C. Williams and R. K. Guy, Some fourth-order linear divisibility sequences, Intl. J. Number Theory 7 (5) (2011) 1255-1277. H. C. Williams and R. K. Guy, Some Monoapparitic Fourth Order Linear Divisibility Sequences Integers, Volume 12A (2012) The John Selfridge Memorial Volume Index entries for linear recurrences with constant coefficients, signature (7,138,112,-256). FORMULA a(n) = (1/9)*(2^n + (-1)^n)*(2^(3*n) - (-1)^n) = (1/9)*(4^n - 1)*(8^n - (-1)^n)/(2^n - (-1)^n). O.g.f.: x*(1 + 28*x + 16*x^2)/((1 - x)*(1 + 2*x)*(1 + 8*x)*(1 - 16*x)). Recurrence equation: a(n) = 7*a(n-1) + 138*a(n-2) + 112*a(n-4) - 256*a(n-4). MAPLE seq(1/9*(2^n + (-1)^n)*(2^(3*n) - (-1)^n), n = 1..20); CROSSREFS Cf. A238536, A238537, A238538, A238540, A238541. Sequence in context: A073567 A225697 A133458 * A075664 A133317 A322879 Adjacent sequences:  A238536 A238537 A238538 * A238540 A238541 A238542 KEYWORD nonn,easy AUTHOR Peter Bala, Mar 01 2014 STATUS approved

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Last modified July 26 13:40 EDT 2021. Contains 346294 sequences. (Running on oeis4.)