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 A228874 L(n) * L(n+1) * L(n+2) * L(n+3), the product of four consecutive Lucas numbers, A000032. 2
 24, 84, 924, 5544, 40194, 269874, 1864584, 12741324, 87431844, 599001144, 4106310474, 28143249834, 192901471224, 1322153872644, 9062210132844, 62113226746824, 425730613530834, 2918000448971874, 20000274149827944, 137083914357154044, 939587137457703924 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Mohanty and Mohanty prove in Corollary 2.6 that these numbers are Pythagorean. The number a(n) is primitive Pythagorean if Lucas(n) and Lucas(n+1) have opposite parity. Every third number, starting at a(1) = 84, is not primitive Pythagorean. Since a(n) = L(n+1)*L(n+2)*(L(n+2)^2-L(n+1)^2), these numbers are in A073120, - Robert Israel, Apr 06 2015 LINKS Robert Israel, Table of n, a(n) for n = 0..1193 Supriya Mohanty and S. P. Mohanty, Pythagorean Numbers, Fibonacci Quarterly 28 (1990), 31-42. Index entries for linear recurrences with constant coefficients, signature (5,15,-15,-5,1). FORMULA G.f.: 6*(x^4-4*x^3-24*x^2+6*x-4) / ((x-1)*(x^2-7*x+1)*(x^2+3*x+1)). - Colin Barker, Oct 29 2013 From Robert Israel, Apr 06 2015 (Start): a(n+5) = 5*a(n+4)+15*a(n+3)-15*a(n+2)-5*a(n+1)+a(n). a(n) = -A228873(n+3)+4*A228873(n+2)+24*A228873(n+1)-6*A228873(n)+4*A228873(n-1) for n >= 2. (End) MAPLE L:= n -> 2*combinat:-fibonacci(n+1)-combinat:-fibonacci(n): seq(mul(L(n+i), i=0..3), n=0..30); # Robert Israel, Apr 06 2015 MATHEMATICA Table[LucasL[n] LucasL[n+1] LucasL[n+2] LucasL[n+3], {n, 0, 25}] Times@@@Partition[LucasL[Range[0, 30]], 4, 1] (* Harvey P. Dale, Jul 11 2017 *) PROG (PARI) Vec(6*(x^4-4*x^3-24*x^2+6*x-4)/((x-1)*(x^2-7*x+1)*(x^2+3*x+1)) + O(x^100)) \\ Colin Barker, Oct 29 2013 CROSSREFS Cf. A000032 (Lucas numbers), A228873 (similar sequence for Fibonacci numbers). Cf. A009112 (Pythagorean numbers), A024365, A073120. Sequence in context: A280304 A168538 A007201 * A211328 A304375 A044211 Adjacent sequences:  A228871 A228872 A228873 * A228875 A228876 A228877 KEYWORD nonn,easy AUTHOR T. D. Noe, Sep 24 2013 STATUS approved

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Last modified August 5 00:15 EDT 2021. Contains 346456 sequences. (Running on oeis4.)