20101021 has 4 divisors (see below), whose sum is σ = 21283452. Its totient is φ = 18918592.

The previous prime is 20101013. The next prime is 20101073. The reversal of 20101021 is 12010102.

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 11978521 + 8122500 = 3461^2 + 2850^2 .

It is a cyclic number.

It is not a de Polignac number, because 20101021 - 2³ = 20101013 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20100995 and 20101013.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20101001) 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, 591190 + ... + 591223.

It is an arithmetic number, because the mean of its divisors is an integer number (5320863).

Almost surely, 2^20101021 is an apocalyptic number.

It is an amenable number.

20101021 is a deficient number, since it is larger than the sum of its proper divisors (1182431).

20101021 is a wasteful number, since it uses less digits than its factorization.

20101021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1182430.

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

The square root of 20101021 is about 4483.4162198038. The cubic root of 20101021 is about 271.8980163013.

Adding to 20101021 its reverse (12010102), we get a palindrome (32111123).

The spelling of 20101021 in words is "twenty million, one hundred one thousand, twenty-one".