21101021 has 8 divisors (see below), whose sum is σ = 21404088. Its totient is φ = 20800000.

The previous prime is 21100999. The next prime is 21101027. The reversal of 21101021 is 12010112.

It can be written as a sum of positive squares in 4 ways, for example, as 13322500 + 7778521 = 3650^2 + 2789^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21101021 - 2²² = 16906717 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21101027) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40241 + ... + 40761.

It is an arithmetic number, because the mean of its divisors is an integer number (2675511).

Almost surely, 2^21101021 is an apocalyptic number.

It is an amenable number.

21101021 is a deficient number, since it is larger than the sum of its proper divisors (303067).

21101021 is a wasteful number, since it uses less digits than its factorization.

21101021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1023.

The product of its (nonzero) digits is 4, while the sum is 8.

The square root of 21101021 is about 4593.5847657358. The cubic root of 21101021 is about 276.3341058242.

Adding to 21101021 its reverse (12010112), we get a palindrome (33111133).

Subtracting from 21101021 its reverse (12010112), we obtain a palindrome (9090909).

The spelling of 21101021 in words is "twenty-one million, one hundred one thousand, twenty-one".