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
KEYWORD
nonn,easy,base
AUTHOR
Bernard Schott, Dec 16 2012
STATUS
approved