21042920 has 16 divisors (see below), whose sum is σ = 47346660. Its totient is φ = 8417152.

The previous prime is 21042919. The next prime is 21042947. The reversal of 21042920 is 2924012.

It can be written as a sum of positive squares in 2 ways, for example, as 17455684 + 3587236 = 4178^2 + 1894^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21042892 and 21042901.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 262997 + ... + 263076.

Almost surely, 2^21042920 is an apocalyptic number.

21042920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21042920 is an abundant number, since it is smaller than the sum of its proper divisors (26303740).

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

21042920 is a wasteful number, since it uses less digits than its factorization.

21042920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 526084 (or 526080 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21042920 is about 4587.2562605549. The cubic root of 21042920 is about 276.0802469173.

Adding to 21042920 its reverse (2924012), we get a palindrome (23966932).

The spelling of 21042920 in words is "twenty-one million, forty-two thousand, nine hundred twenty".