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A038521
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Number of elements of GF(2^n) with trace 1 and subtrace 1.
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5
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0, 2, 1, 4, 10, 12, 36, 64, 120, 272, 496, 1024, 2080, 4032, 8256, 16384, 32640, 65792, 130816, 262144, 524800, 1047552, 2098176, 4194304, 8386560, 16781312, 33550336, 67108864, 134225920, 268419072, 536887296, 1073741824, 2147450880
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = C(n, r+0) + C(n, r+4) + C(n, r+8) + ... where r = 3 if n odd, r = 1 if n even.
G.f.: x*(2 + x) / ((1 - 2*x)*(1 + 2*x + 2*x^2)).
a(n) = ((-1-i)^(-1+n) + (-1+i)^(-1+n) + 2^n) / 2.
a(n) = 2*a(n-2) + 4*a(n-3) for n>2.
(End)
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MAPLE
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A038521 := proc(n) local r, a, i ; if n mod 2 = 1 then r := 3 ; else r := 1 ; fi; a :=0 ; for i from r to n by 4 do a := a+binomial(n, i) ; od; a ; end: for n from 1 to 40 do printf("%d, ", A038521(n)) ; od: # R. J. Mathar, Oct 20 2008
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MATHEMATICA
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PROG
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(PARI) concat(0, Vec(x*(2 + x) / ((1 - 2*x)*(1 + 2*x + 2*x^2)) + O(x^35))) \\ Colin Barker, Aug 02 2019
(Magma) I:=[0, 2, 1]; [m le 3 select I[m] else 2*Self(m-2) + 4*Self(m-3): m in [1..33]] // Marius A. Burtea, Aug 02 2019
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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