21121121

Appears in sequences

• Smallest natural number requiring n words in English (as spoken in England).at n=13A001167
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,1.at n=7A037559
• Pseudoprimes to base 3, written in base 3.at n=18A258189
• Smallest positive integer whose American English name consists of n words.at n=11A356738