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A173951 Positive integers with the property that if the base-3 representation is reversed the result is twice the original number. 4
32, 104, 320, 968, 2624, 2912, 7808, 8744, 23360, 25376, 26240, 70016, 75920, 78728, 209984, 212576, 227552, 233600, 236192, 629888, 638312, 682448, 700160, 708584, 1889600, 1897376, 1915520, 2047136, 2054912, 2099840, 2117984, 2125760 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The number of terms of this sequence containing n ternary digits is given by {d(n)}={0,0,0,1,1,1,1,2,2,3,3,5,5,8,8,13,13,21,...} for n=1,2,3,... and thus appears to be essentially the doubling-up of the Fibonacci numbers A103609. For example, 2624 = 10121012(base-3) and 2912 = 10222212(base-3) are the only two terms that have 8 digits when written in base 3, so d(8)=2.

(This conjecture is correct - see A223077. - N. J. A. Sloane, Mar 19 2013)

All terms of sequence A173952, defined by b(1)=32 and, for n>1, b(n)=9*b(n-1)+32, appear to be terms of the above sequence {a(n)}; in fact each term b(n) appears to be the largest term of {a(k)} that has 2n+2 digits when written in base 3.

LINKS

Table of n, a(n) for n=1..32.

CROSSREFS

Cf. A103609, A173952, A223077, A214927.

Sequence in context: A134845 A167982 A063498 * A233691 A233684 A218068

Adjacent sequences:  A173948 A173949 A173950 * A173952 A173953 A173954

KEYWORD

nonn,base

AUTHOR

John W. Layman, Mar 03 2010

STATUS

approved

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Last modified July 21 12:27 EDT 2017. Contains 289642 sequences.