21001220121 has 96 divisors (see below), whose sum is σ = 35006227200. Its totient is φ = 11187052800.

The previous prime is 21001220099. The next prime is 21001220153. The reversal of 21001220121 is 12102210012.

It is not a de Polignac number, because 21001220121 - 2¹⁰ = 21001219097 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21001220097 and 21001220106.

It is not an unprimeable number, because it can be changed into a prime (21001220171) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 22317511 + ... + 22318451.

It is an arithmetic number, because the mean of its divisors is an integer number (364648200).

Almost surely, 2^21001220121 is an apocalyptic number.

21001220121 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21001220121 is a deficient number, since it is larger than the sum of its proper divisors (14005007079).

21001220121 is an equidigital number, since it uses as much as digits as its factorization.

21001220121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1052 (or 1015 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 12.

Adding to 21001220121 its reverse (12102210012), we get a palindrome (33103430133).

It can be divided in two parts, 2100 and 1220121, that added together give a palindrome (1222221).

The spelling of 21001220121 in words is "twenty-one billion, one million, two hundred twenty thousand, one hundred twenty-one".