21010101021 has 24 divisors (see below), whose sum is σ = 37351292160. Its totient is φ = 11082250656.

The previous prime is 21010100971. The next prime is 21010101041. The reversal of 21010101021 is 12010101012.

It is a happy number.

It is not a de Polignac number, because 21010101021 - 2⁷ = 21010100893 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21010100994 and 21010101012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21010101041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 12825861 + ... + 12827498.

It is an arithmetic number, because the mean of its divisors is an integer number (1556303840).

Almost surely, 2^21010101021 is an apocalyptic number.

21010101021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21010101021 is a deficient number, since it is larger than the sum of its proper divisors (16341191139).

21010101021 is a wasteful number, since it uses less digits than its factorization.

21010101021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25653385 (or 25653382 counting only the distinct ones).

The product of its (nonzero) digits is 4, while the sum is 9.

Adding to 21010101021 its reverse (12010101012), we get a palindrome (33020202033).

Subtracting from 21010101021 its reverse (12010101012), we obtain a palindrome (9000000009).

The spelling of 21010101021 in words is "twenty-one billion, ten million, one hundred one thousand, twenty-one".