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 A124870 Denominator of real part of (2*omega)^(-n) where omega = (-1 + i*3)/ 2. 4
 1, 10, 25, 500, 2500, 25000, 31250, 1250000, 6250000, 62500000, 78125000, 3125000000, 15625000000, 156250000000, 195312500000, 7812500000000, 39062500000000, 390625000000000, 488281250000000, 19531250000000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS See A124869 for comments and references. LINKS FORMULA a(n) = denominator(Re(1/(-1 + i*3)^n) ). 1/(-1 + i*3)^n = A124869(n)/ A124870(n) + i*A124871(n)/A124872(n). Conjectures from Colin Barker, Jul 16 2019: (Start) G.f.: (1 + 10*x + 25*x^2 + 500*x^3 - 31250*x^6) / ((1 - 50*x^2)*(1 + 50*x^2)). a(n) = 2500*a(n-4) for n>6. (End) EXAMPLE a(0) = 1 = denominator of Re((-1+3*i)^0) = 1/1 + 0*i. a(1) = 10 = denominator of Re(1/(-1+3*i)) = -1/10 - i*3/10. a(2) = 25 = denominator of Re((-1+3*i)^(-2)) = -2/25 + i*3/50. a(3) = 500 = denominator of Re((-1+3*i)^(-3)) = 13/500 + i*9/500. a(4) = 2500 = denominator of Re((-1+3*i)^(-4)) = 7/2500 - i*6/625. a(5) = 25000 = denominator of Re((-1+3*i)^(-5)) = -79/25000 + i*3/25000. a(6) = 31250 = denominator of Re((-1+3*i)^(-6)) = 11/31250 + i*117/125000. CROSSREFS Cf. A124869-A124872. Sequence in context: A220039 A219377 A156183 * A078257 A059198 A259297 Adjacent sequences: A124867 A124868 A124869 * A124871 A124872 A124873 KEYWORD easy,frac,nonn AUTHOR Jonathan Vos Post, Nov 11 2006 EXTENSIONS Removed square roots from definition and formula. - R. J. Mathar, May 02 2009 STATUS approved

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Last modified December 6 10:38 EST 2022. Contains 358630 sequences. (Running on oeis4.)