122222221

Appears in sequences

• All possible products in increasing order of two distinct members of the unary sequence 1, 11, 111, 1111, 11111, ...given by A000042.at n=17A077488
• Expansion of g.f. x*(1+10*x)/((1-x)*(1-10*x^2)).at n=16A094623
• Expansion of g.f. x*(1+11*x+x^2)/((1-x)*(1+x)*(1-10*x^2)).at n=16A094624
• a(n) = n 2's sandwiched between two 1's.at n=7A132583
• Palindromes p=A002113(n) whose index n is also a palindrome and in addition a substring of p (strings in base 10).at n=23A248754
• Numbers that can be written as a product of distinct repunits.at n=21A334131
• a(1) = 1; for n > 1, a(n) is the smallest unused positive number such that a(n), |a(n) - a(n-1)| and a(1) + ... +a(n) are all palindromes.at n=38A376856