21011920 has 20 divisors (see below), whose sum is σ = 48852900. Its totient is φ = 8404736.

The previous prime is 21011917. The next prime is 21011923. The reversal of 21011920 is 2911012.

It is an interprime number because it is at equal distance from previous prime (21011917) and next prime (21011923).

It can be written as a sum of positive squares in 2 ways, for example, as 11451456 + 9560464 = 3384^2 + 3092^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a junction number, because it is equal to n+sod(n) for n = 21011894 and 21011903.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011923) 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, 131245 + ... + 131404.

It is an arithmetic number, because the mean of its divisors is an integer number (2442645).

Almost surely, 2^21011920 is an apocalyptic number.

21011920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21011920 is an abundant number, since it is smaller than the sum of its proper divisors (27840980).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21011920 is a wasteful number, since it uses less digits than its factorization.

21011920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 262662 (or 262656 counting only the distinct ones).

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21011920 is about 4583.8760890757. The cubic root of 21011920 is about 275.9446083617.

Adding to 21011920 its reverse (2911012), we get a palindrome (23922932).

The spelling of 21011920 in words is "twenty-one million, eleven thousand, nine hundred twenty".