OFFSET
0,1
COMMENTS
The sequence is well defined and zero for n sufficiently large (> 6.1*10^30 ?) because "million", "billion" etc. have a letter in common with all small numbers except for three, which is letter-disjoint with six. Therefore, 3 is letter-disjoint with six, six million, six billion, six nonillion (10^30) and any nonempty sum of two or more of these. See also example of a(5).
LINKS
E. Angelini, Chaîne de noms de nombres
E. Angelini, Chaîne de noms de nombres [Cached copy, with permission]
EXAMPLE
a(0) = 5 = # {6, 50, 56, 60, 66} because "zero" has no letter in common with: six, fifty, fifty-six, sixty, sixty-six.
a(5) = 3 = # {2, 2000, 2002} because "five" has no letter in common with: two, two thousand, two thousand two. ("thousand" is not considered; "one thousand" is excluded.)
a(3) = 15 = 2^4-1 because any nonzero sum_{i=0,6,9,30} e_i*10^i with e_i in {0, 6} is "letter-disjoint" with three.
PROG
CROSSREFS
KEYWORD
nonn,word
AUTHOR
M. F. Hasler, Nov 04 2013
STATUS
approved