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Search: id:A090129
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| A090129 |
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Smallest exponent such that -1+3^a[n] is divisible by 2^n. |
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+0
8
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| 1, 2, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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A152046=1,1,1,3,5,11,=1,A001045(n+1)?. a(n+1)=A152046(n)+A152406(n+1)=2*A011782. A131577 and A011782 are companions, A131577+A011782=2^n=A000079, (and differences each other). [From Paul Curtz (bpcrtz(AT)free.fr), Jan 18 2009]
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EXAMPLE
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a[1]=1 since -1+3=2 is divisible by 2^1;
a[2]=a[3]=2 since -1+9=8 is divisible by 4=2^2 and also by 8=2^3;
a[5]=8 since -1+6561=6560=32.205 is divisible by 2^5.
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MATHEMATICA
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t=Table[Part[Flatten[FactorInteger[ -1+3^(n)]], 2], {n, 1, 130}] Table[Min[Flatten[Position[t, j]]], {j, 1, 10}]
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CROSSREFS
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Cf. A069895, A091512, A088660, A090739, A090740.
Sequence in context: A054243 A005864 A112433 this_sequence A001137 A123593 A122748
Adjacent sequences: A090126 A090127 A090128 this_sequence A090130 A090131 A090132
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KEYWORD
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nonn
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AUTHOR
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Labos E. and R. Stephan ((labos(AT)ana.sote.hu) and (ralf(AT)ark.in-berlin.de)), Jan 19 2004
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EXTENSIONS
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a(11) through a(20) by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 08 2008
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