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A220570 Numbers that are not Brazilian numbers. 19
1, 2, 3, 4, 5, 6, 9, 11, 17, 19, 23, 25, 29, 37, 41, 47, 49, 53, 59, 61, 67, 71, 79, 83, 89, 97, 101, 103, 107, 109, 113, 131, 137, 139, 149, 151, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 223, 227, 229, 233, 239, 251, 257, 263, 269, 271, 277, 281 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
From Bernard Schott, Apr 23 2019: (Start)
The terms of this sequence are:
- integer 1
- oblong semiprime 6,
- primes that are not Brazilian, they are in A220627, and,
- squares of all the primes, except 121 = (11111)_3.
So there is an infinity of integers that are not Brazilian numbers. (End)
This sequence has density 0 as A125134(n) ~ n where A125134 is the complement of this sequence. - David A. Corneth, Jan 22 2021
REFERENCES
Pierre Bornsztein, "Hypermath", Vuibert, Exercise a35, page 7.
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe)
Bernard Schott, Les nombres brésiliens, Quadrature, no. 76, avril-juin 2010, &6 page 36; included here with permission from the editors of Quadrature.
EXAMPLE
25 is a member because it's not possible to write 25=(mm...mm)_b where b is a natural number with 1 < b < 24 and 1 <= m < b.
PROG
(PARI) for(n=1, 300, c=0; for(b=2, n-2, d=digits(n, b); if(vecmin(d)==vecmax(d), c=n; break); c++); if(c==max(n-3, 0), print1(n, ", "))) \\ Derek Orr, Apr 30 2015
CROSSREFS
Cf. A125134 (Brazilian numbers), A190300 (composite numbers not Brazilian), A258165 (odd numbers not Brazilian), A220627 (prime numbers not Brazilian).
Sequence in context: A102571 A251241 A064278 * A341057 A299297 A325323
KEYWORD
nonn,easy,base
AUTHOR
Bernard Schott, Dec 16 2012
STATUS
approved

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)