21143720 has 64 divisors (see below), whose sum is σ = 52027920. Its totient is φ = 7686144.

The previous prime is 21143719. The next prime is 21143723. The reversal of 21143720 is 2734112.

It can be written as a sum of positive squares in 8 ways, for example, as 1976836 + 19166884 = 1406^2 + 4378^2 .

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 = 21143692 and 21143701.

It is not an unprimeable number, because it can be changed into a prime (21143723) 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, 37682 + ... + 38238.

Almost surely, 2^21143720 is an apocalyptic number.

21143720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21143720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26013960).

21143720 is an abundant number, since it is smaller than the sum of its proper divisors (30884200).

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

21143720 is a wasteful number, since it uses less digits than its factorization.

21143720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 654 (or 650 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 20.

The square root of 21143720 is about 4598.2300942863. The cubic root of 21143720 is about 276.5203723271.

Adding to 21143720 its reverse (2734112), we get a palindrome (23877832).

The spelling of 21143720 in words is "twenty-one million, one hundred forty-three thousand, seven hundred twenty".