

A288783


Brazilian numbers which have only one Brazilian representation.


4



7, 8, 10, 12, 13, 14, 16, 20, 22, 27, 33, 34, 35, 38, 39, 43, 46, 51, 55, 58, 65, 69, 73, 74, 77, 81, 82, 87, 94, 95, 106, 115, 118, 119, 121, 122, 123, 125, 127, 134, 141, 142, 143, 145
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OFFSET

1,1


COMMENTS

These numbers could be called 1Brazilian numbers.
The smallest number of this sequence is 7 = 111_2 which is also the smallest Brazilian number (A125134) and so the smallest Brazilian prime (A085104).
a(2) = 8 is the smallest composite Brazilian number and so the smallest even composite Brazilian with 8 = 22_3 (A220571).
a(10) = 27 is the smallest odd composite Brazilian in this sequence because 27 = 33_8 but 15 is the smallest odd composite Brazilian with 15 = 1111_2 = 33_4 so with two representations.
121 is the only square of prime which is Brazilian with 121 = 11111_3.
In this sequence, there are:
1) The Brazilian primes and the lone square prime 121 which are all repunits in a base >= 2 with a string of at least three 1's.
2) The composite numbers which are such that n = a * b = (aa)_(b1) with 1 < a < b1 with only one such product a * b.


REFERENCES

D. Lignon, Dictionnaire de (presque) tous les nombres entiers, Ellipses, 2012, page 420.


LINKS

Table of n, a(n) for n=1..44.
Bernard Schott, Les nombres brésiliens, Quadrature, no. 76, avriljuin 2010, pages 3038.


EXAMPLE

13 = 111_3; 127 = 1111111_2.
20 = 2 * 10 = 22_9; 55 = 5 * 11 = 55_10; 69 = 3 * 23 = 33_22.


MATHEMATICA

Select[Range@ 145, Function[n, Count[Range[2, n  2], b_ /; SameQ @@ IntegerDigits[n, b]] == 1]] (* Michael De Vlieger, Jun 16 2017 *)


CROSSREFS

Cf. A085104, A125134, A190300, A220570, A220571, A253260, A284758.
Sequence in context: A037263 A125134 A169876 * A120175 A291668 A175222
Adjacent sequences: A288780 A288781 A288782 * A288784 A288785 A288786


KEYWORD

nonn,base,easy


AUTHOR

Bernard Schott, Jun 15 2017


STATUS

approved



