OFFSET
1,1
COMMENTS
a(1) = 0 is forbidden as [0 x a(n)] = 0, a term of the sequence;
a(1) = 1 is forbidden as [1 x a(n)] = a(n), a term of the sequence;
a(1) = 2 is ok;
a(2) = 3 is ok;
a(3) = 4 is ok, but no more digits 2 as (2 x 2) = 4;
a(4) = 5 is ok as (5 x 2), (5 x 3), (5 x 4)... are > 9;
a(5) = 6 is forbidden as (2 x 3) = 6;
a(5) = 7 is ok as (7 x 2), (7 x 3), (7 x 4)... are > 9;
a(6) = 8 is forbidden as (2 x 4) = 8;
a(6) = 9 is ok, but no more digits 3 as (3 x 3) = 9.
The other terms of the sequence use only digits 4,5,7 and 9.
LINKS
Jean-Marc Falcoz, Table of n, a(n) for n = 1..1002
EXAMPLE
2 x 3 = 6 and there is no term or digit 6 in the sequence;
2 x 4 = 8 and there is no term or digit 8 in the sequence;
2 x 5 = 10 and there is no term 10 in the sequence;
2 x 6 = 12 and there is no term 12 in the sequence;
2 x 7 = 14 and there is no term 14 in the sequence;
2 x 9 = 18 and there is no term 18 in the sequence;
3 x 4 = 12 and there is no term 12 in the sequence;
3 x 5 = 15 and there is no term 15 in the sequence;
etc.
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jean-Marc Falcoz and Eric Angelini, Apr 16 2018
STATUS
approved