12222221

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=13A077488
• Expansion of g.f. x*(1+10*x)/((1-x)*(1-10*x^2)).at n=14A094623
• Expansion of g.f. x*(1+11*x+x^2)/((1-x)*(1+x)*(1-10*x^2)).at n=14A094624
• Divisors of 10^14 - 1.at n=25A106305
• a(n) = n 2's sandwiched between two 1's.at n=6A132583
• Numbers k such that gcd(k^2, reverse(k^2)) = k.at n=33A175823
• Algebraic cofactor of n-th repunit A002275(n).at n=13A204848
• Numbers which are products of repunits.at n=31A308365
• Numbers that can be written as a product of distinct repunits.at n=16A334131
• 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=33A376856