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A151821
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Powers of 2, omitting 2 itself.
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29
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1, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648, 4294967296, 8589934592
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OFFSET
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1,2
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COMMENTS
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An elephant sequence, see A175655. For the central square just one A[5] vector, with decimal value 170, leads to this sequence. For the corner squares this vector leads to the companion sequence A095121. - Johannes W. Meijer, Aug 15 2010
This is a subsequence of A055744, numbers n such that n and phi(n) have same prime factors. - Michel Marcus, Mar 20 2015
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LINKS
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FORMULA
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a(1) = 1 and a(n) = 3 + Sum_{k=1..n-1} a(k) for n>=2. - Joerg Arndt, Aug 15 2012
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MATHEMATICA
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CoefficientList[Series[(1 + 2 x)/(1 - 2 x), {x, 0, 40}], x] (* Vincenzo Librandi, Jul 21 2013
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PROG
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(Haskell)
a151821 n = a151821_list !! (n-1)
a151821_list = x : xs where (x : _ : xs) = a000079_list
(PARI) Vec(x*(1+2*x)/(1-2*x) + O(x^100)) \\ Altug Alkan, Dec 09 2015
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CROSSREFS
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Partial sums are given by 2*A000225(n)-1, which is not the same as A000918.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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