211111111
domain: N
Appears in sequences
- a(1) = 1, then the smallest number not included earlier and not a string of 1's such that the concatenation a(n), a(n+1) is a palindrome.at n=30A083122
- Smallest semiprime ending in exactly n 1's.at n=7A106656
- Over the alphabet {1,2} let A=111, B=211; sequence lists words A, B, AA, AB, BA, BB, AAA, AAB, ...at n=10A291797