21111220121 has 4 divisors (see below), whose sum is σ = 21122529552. Its totient is φ = 21099910692.

The previous prime is 21111220111. The next prime is 21111220127. The reversal of 21111220121 is 12102211112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21111220121 - 2¹⁰ = 21111219097 is a prime.

It is a super-2 number, since 2×21111220121² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21111220096 and 21111220105.

It is not an unprimeable number, because it can be changed into a prime (21111220127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5651915 + ... + 5655648.

It is an arithmetic number, because the mean of its divisors is an integer number (5280632388).

Almost surely, 2^21111220121 is an apocalyptic number.

It is an amenable number.

21111220121 is a deficient number, since it is larger than the sum of its proper divisors (11309431).

21111220121 is a wasteful number, since it uses less digits than its factorization.

21111220121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11309430.

The product of its (nonzero) digits is 16, while the sum is 14.

Adding to 21111220121 its reverse (12102211112), we get a palindrome (33213431233).

Subtracting from 21111220121 its reverse (12102211112), we obtain a palindrome (9009009009).

The spelling of 21111220121 in words is "twenty-one billion, one hundred eleven million, two hundred twenty thousand, one hundred twenty-one".