20100021 has 4 divisors (see below), whose sum is σ = 26800032. Its totient is φ = 13400012.

The previous prime is 20099983. The next prime is 20100023. The reversal of 20100021 is 12000102.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20100021 - 2¹⁹ = 19575733 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20099982 and 20100009.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20100023) 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, 3350001 + ... + 3350006.

It is an arithmetic number, because the mean of its divisors is an integer number (6700008).

Almost surely, 2^20100021 is an apocalyptic number.

It is an amenable number.

20100021 is a deficient number, since it is larger than the sum of its proper divisors (6700011).

20100021 is an equidigital number, since it uses as much as digits as its factorization.

20100021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6700010.

The product of its (nonzero) digits is 4, while the sum is 6.

The square root of 20100021 is about 4483.3046963150. The cubic root of 20100021 is about 271.8935073674.

Adding to 20100021 its reverse (12000102), we get a palindrome (32100123).

The spelling of 20100021 in words is "twenty million, one hundred thousand, twenty-one".