OFFSET
1,2
COMMENTS
This sequence lists the positions of nonzero digits in the sequence, where the terms are written in base 3 and concatenated, such that the least significant digit (units) of a(n) is followed by the most significant digit of a(n+1).
EXAMPLE
The list cannot start with 0 (cf. A167500), so the first digit of the sequence is nonzero, whence a(1)=1.
The next nonzero digit of this sequence will be the most significant digit (m.s.d.) of a(2), necessarily nonzero, thus a(2)=2.
For the same reason, a(3) = 3[10] = 10[3]. (All terms are written in base 3.)
Thus the 4th digit is zero, followed by the m.s.d. of the next term which is nonzero, thus a(4)=5.
Terms of the sequence:_ 1,2,10,12,20,21,100,101
Position of the digits: 1 2 34 56 78 9A BCD EFG (A=10,...)
Thus the numbers 4,8,12,13,15,..., which give the positions of digits '0', are not in this sequence.
PROG
(PARI) base(n, b=3, s=1) = { my( a=[ n%b ]); while( 0<n\=b, a=concat( n%b, a )); if( s, eval( Strchr( vectorsmall( #a, i, 48+a[i] ))), a) }
{a=b=[]; for(n=1, 99, #b>=n & for(i=a[n-1]+1, #b, b[i] & (a=concat(a, i)) & break); #a<n & a=concat(a, #b+1); b=concat(b, base(a[n], 3, 0))); apply(base, a)}
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Nov 05 2009
EXTENSIONS
Edited by Charles R Greathouse IV, Aug 02 2010
STATUS
approved