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1, -4, 16, -64, 256, -1024, 4096, -16384, 65536, -262144, 1048576, -4194304, 16777216, -67108864, 268435456, -1073741824, 4294967296, -17179869184, 68719476736, -274877906944, 1099511627776, -4398046511104, 17592186044416, -70368744177664, 281474976710656
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refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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COMMENTS
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Purely real values from the sequence generated by (1 + i)^k where i = sqrt(-1) and k is a real nonnegative integer.
This sequence gives the values of (1 + i)^k when k is a multiple of 4. When k = 2 mod 4, (1 + i)^k is purely imaginary, and when k is odd, (1 + i)^k has both a real and an imaginary part, and abs(Re((1 + i)^k)) = abs(Im((1 + i)^k)).
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (-4).
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FORMULA
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a(n) = (-4)^n.
G.f.: 1/(1 + 4 * x).
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MATHEMATICA
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(-4)^Range[0, 15] (* Alonso del Arte, Mar 16 2016 *)
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PROG
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(PARI) vector(100, n, n--; (-4)^n) \\ Altug Alkan, Oct 05 2015
(PARI) Vec(1/(1+4*x) + O(x^30)) \\ Michel Marcus, Oct 06 2015
(PARI) lista(nn) = for (n=0, nn, z = (1+I)^n; if (imag(z)==0, print1(real(z), ", "))); \\ Michel Marcus, Nov 01 2015
(MAGMA) [(-1)^n*4^n: n in [0..30]]; // Vincenzo Librandi, Oct 06 2015
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CROSSREFS
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Cf. A000302, A016825, A005408, A122803.
Sequence in context: A294452 A270142 A000302 * A050734 A075614 A083592
Adjacent sequences: A262707 A262708 A262709 * A262711 A262712 A262713
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KEYWORD
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sign,easy
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AUTHOR
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L. Van Warren, Sep 28 2015
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STATUS
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approved
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