21000001021 has 4 divisors (see below), whose sum is σ = 21185841852. Its totient is φ = 20814160192.

The previous prime is 21000001013. The next prime is 21000001069. The reversal of 21000001021 is 12010000012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4388400025 + 16611600996 = 66245^2 + 128886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000001021 - 2³ = 21000001013 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21000000995 and 21000001013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000001091) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 92920246 + ... + 92920471.

It is an arithmetic number, because the mean of its divisors is an integer number (5296460463).

Almost surely, 2^21000001021 is an apocalyptic number.

It is an amenable number.

21000001021 is a deficient number, since it is larger than the sum of its proper divisors (185840831).

21000001021 is a wasteful number, since it uses less digits than its factorization.

21000001021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 185840830.

The product of its (nonzero) digits is 4, while the sum is 7.

Adding to 21000001021 its reverse (12010000012), we get a palindrome (33010001033).

The spelling of 21000001021 in words is "twenty-one billion, one thousand, twenty-one".