112123

Appears in sequences

• Sorted list of strings that can be obtained by starting with 123 and repeatedly doubling any substring in place.at n=15A135475
• Triangle read by rows: left edge is all 1's, right edge is 1, 2, 3, 4, ...; construct an internal entry by concatenating the two entries above it.at n=12A213057
• Number of (n+3) X 6 0..1 matrices with each 4 X 4 subblock idempotent.at n=21A224563