21123720 has 64 divisors (see below), whose sum is σ = 70416000. Its totient is φ = 5632704.

The previous prime is 21123709. The next prime is 21123721. The reversal of 21123720 is 2732112.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21123693 and 21123702.

It is not an unprimeable number, because it can be changed into a prime (21123721) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8700 + ... + 10859.

It is an arithmetic number, because the mean of its divisors is an integer number (1100250).

Almost surely, 2^21123720 is an apocalyptic number.

21123720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21123720 is an abundant number, since it is smaller than the sum of its proper divisors (49292280).

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

21123720 is a wasteful number, since it uses less digits than its factorization.

21123720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19579 (or 19569 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 21123720 is about 4596.0548299601. The cubic root of 21123720 is about 276.4331572720.

Adding to 21123720 its reverse (2732112), we get a palindrome (23855832).

It can be divided in two parts, 2112 and 3720, that added together give a cube (5832 = 18³).

The spelling of 21123720 in words is "twenty-one million, one hundred twenty-three thousand, seven hundred twenty".