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A272919
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Numbers of the form 2^(n-1)*(2^(n*m)-1)/(2^n-1), n >= 1, m >= 1.
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140
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1, 2, 3, 4, 7, 8, 10, 15, 16, 31, 32, 36, 42, 63, 64, 127, 128, 136, 170, 255, 256, 292, 511, 512, 528, 682, 1023, 1024, 2047, 2048, 2080, 2184, 2340, 2730, 4095, 4096, 8191, 8192, 8256, 10922, 16383, 16384, 16912, 18724, 32767, 32768, 32896, 34952, 43690, 65535, 65536, 131071
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OFFSET
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1,2
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COMMENTS
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In other words, numbers whose binary representation consists of one or more repeating blocks with only one 1 in each block.
Each a(n) is a term of A064896 multiplied by some power of 2. As such, this sequence must also be a subsequence of A125121.
Also the numbers that uniquely index a Haar graph (i.e., 5 and 6 are not in the sequence since H(5) is isomorphic to H(6)). - Eric W. Weisstein, Aug 19 2017
The k-th composition in standard order (row k of A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions. This sequence lists all positive integers k such that the k-th composition in standard order is constant. For example, the sequence together with the corresponding constant compositions begins:
0: () 136: (4,4)
1: (1) 170: (2,2,2,2)
2: (2) 255: (1,1,1,1,1,1,1,1)
3: (1,1) 256: (9)
4: (3) 292: (3,3,3)
7: (1,1,1) 511: (1,1,1,1,1,1,1,1,1)
8: (4) 512: (10)
10: (2,2) 528: (5,5)
15: (1,1,1,1) 682: (2,2,2,2,2)
16: (5) 1023: (1,1,1,1,1,1,1,1,1,1)
31: (1,1,1,1,1) 1024: (11)
32: (6) 2047: (1,1,1,1,1,1,1,1,1,1,1)
36: (3,3) 2048: (12)
42: (2,2,2) 2080: (6,6)
63: (1,1,1,1,1,1) 2184: (4,4,4)
64: (7) 2340: (3,3,3,3)
127: (1,1,1,1,1,1,1) 2730: (2,2,2,2,2,2)
128: (8) 4095: (1,1,1,1,1,1,1,1,1,1,1,1)
(End)
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LINKS
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FORMULA
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If n is a power of two, A333628(a(n)) = 0, otherwise = 1.
(End)
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MAPLE
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N:= 10^6: # to get all terms <= N
R:= select(`<=`, {seq(seq(2^(n-1)*(2^(n*m)-1)/(2^n-1), m = 1 .. ilog2(2*N)/n), n = 1..ilog2(2*N))}, N):
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MATHEMATICA
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Flatten@Table[d = Reverse@Divisors[n]; 2^(d - 1)*(2^n - 1)/(2^d - 1), {n, 17}]
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CROSSREFS
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Cf. A137706 (smallest number indexing a new Haar graph).
Compositions in standard order are A066099.
Strict compositions are ranked by A233564.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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