OFFSET
1,3
COMMENTS
All such bases are divisors of n or n-1, since the lowest base-B digit of n is 0 iff B | n, 1 iff B | n-1. - Robert Israel, Jul 04 2018
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(30)=5, since 30 written in the 5 bases 2, 3, 5, 29, 30 is 11110, 1010, 110, 11, 10.
MAPLE
f:= n ->
nops(select(b -> convert(convert(n, base, b), set) subset {0, 1}, {$2..n} intersect (numtheory:-divisors(n) union numtheory:-divisors(n-1)))):
map(f, [$1..200]); # Robert Israel, Jul 04 2018
MATHEMATICA
a[1]=0; a[n_] := Length[Select[Rest[Union[Divisors[n], Divisors[n-1]]], Max@@IntegerDigits[n, # ]==1&]]
PROG
(PARI) a(n) = sum(b=2, n, #select(x->(x>1), digits(n, b)) == 0); \\ Michel Marcus, Jul 04 2018
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Dean Hickerson, Mar 31 2002
STATUS
approved