21020120021 has 4 divisors (see below), whose sum is σ = 21173551692. Its totient is φ = 20866688352.

The previous prime is 21020119963. The next prime is 21020120041. The reversal of 21020120021 is 12002102012.

It is a happy number.

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 9802980100 + 11217139921 = 99010^2 + 105911^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020120021 - 2¹⁰ = 21020118997 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21020119984 and 21020120011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020120041) 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, 76715630 + ... + 76715903.

It is an arithmetic number, because the mean of its divisors is an integer number (5293387923).

Almost surely, 2^21020120021 is an apocalyptic number.

It is an amenable number.

21020120021 is a deficient number, since it is larger than the sum of its proper divisors (153431671).

21020120021 is a wasteful number, since it uses less digits than its factorization.

21020120021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153431670.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21020120021 its reverse (12002102012), we get a palindrome (33022222033).

The spelling of 21020120021 in words is "twenty-one billion, twenty million, one hundred twenty thousand, twenty-one".