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A220571 Composite numbers that are Brazilian. 9
8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There are just two differences of members with A080257:

1) the term 6 is missing here because 6 is not a Brazilian number.

2) the new term 121 is present although 121 has only 3 divisors, because 121 = 11^2 = 11111_3 is a composite number which is Brazilian. 121 is the lone square of a prime which is Brazilian: Theorem 5, page 37 of Quadrature article in links.

There is an infinity of Brazilian composite numbers (Theorem 1, page 32 of Quadrature article in links: every even number >= 8 is a Brazilian number).

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Bernard Schott, Les nombres brésiliens, Quadrature, no. 76, avril-juin 2010, pages 30-38; included here with permission from the editors of Quadrature.

MATHEMATICA

Select[Range[4, 10^2], And[CompositeQ@ #, Module[{b = 2, n = #}, While[And[b < n - 1, Length@ Union@ IntegerDigits[n, b] > 1], b++]; b < n - 1]] &] (* Michael De Vlieger, Jul 30 2017, after T. D. Noe at A125134 *)

CROSSREFS

Cf. A125134, A190300.

Sequence in context: A046031 A102758 A176815 * A033872 A080752 A262159

Adjacent sequences:  A220568 A220569 A220570 * A220572 A220573 A220574

KEYWORD

nonn

AUTHOR

Bernard Schott, Dec 16 2012

STATUS

approved

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Last modified August 22 03:22 EDT 2017. Contains 290942 sequences.