0,3

After 11 we can see 1,2 -> 12, 1,3 ->13, etc., but not 20.

Table of n, a(n) for n=0..69.

Hannah Rollman's numbers: A048991, A048992.

Sequence in context: A247758 A247757 A247754 * A032873 A072543 A009996

Adjacent sequences: A084380 A084381 A084382 * A084384 A084385 A084386

nonn,base

Amarnath Murthy, May 29 2003.

More terms from Patrick De Geest, Jun 03 2003.

approved