A220570 Numbers that are not Brazilian numbers.

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

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

Adjacent sequences: A220567 A220568 A220569 * A220571 A220572 A220573

Keyword

nonn,easy,base

Author

Bernard Schott, Dec 16 2012

Status

approved