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A090129 Smallest exponent such that -1+3^a[n] is divisible by 2^n. +0
3
1, 2, 2, 4, 8, 16, 32, 64, 128, 256 (list; graph; listen)
OFFSET

1,2

EXAMPLE

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.

MATHEMATICA

t=Table[Part[Flatten[FactorInteger[ -1+3^(n)]], 2], {n, 1, 130}] Table[Min[Flatten[Position[t, j]]], {j, 1, 10}]

CROSSREFS

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

KEYWORD

nonn

AUTHOR

Labos E. and R. Stephan ((labos(AT)ana.sote.hu) and (ralf(AT)ark.in-berlin.de)), Jan 19 2004

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Last modified July 26 13:41 EDT 2008. Contains 142293 sequences.


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