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Search: id:A166577
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| 1, 4, -5, 10, -20, 40, -80, 160, -320, 640, -1280, 2560, -5120, 10240, -20480, 40960, -81920, 163840, -327680, 655360, -1310720, 2621440, -5242880, 10485760, -20971520, 41943040, -83886080, 167772160, -335544320, 671088640, -1342177280, 2684354560, -5368709120
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OFFSET
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0,2
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COMMENT
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The definition assumes that the offset of A166517 is changed to 0.
A166517 mod 9 yields a periodic sequence with period 1, 5, 4, 8, 7, 2.
This set of numbers in the period appears also in A153130, A146501, and A166304.
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FORMULA
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a(n)= -2*a(n-1), n>2.
a(n)= (-1)^(n+1)*A020714(n-2), n>1.
a(n)=(9/4)*{1-[(n+2) mod (n+1)]}+(3/2)*{C[(n+1)^2,n+3] mod 2}-5*(-2)^(n-2), with n>=0 [From Paolo P. Lava (ppl(AT)spl.at), Nov 02 2009]
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CROSSREFS
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Cf A010716, A010692, A010859
Sequence in context: A049867 A054173 A049898 this_sequence A109675 A052508 A074098
Adjacent sequences: A166574 A166575 A166576 this_sequence A166578 A166579 A166580
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KEYWORD
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sign,easy,new
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AUTHOR
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Paul Curtz (bpcrtz(AT)free.fr), Oct 17 2009
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EXTENSIONS
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Edited, comments not concerning this sequence removed, and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 21 2009
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