20721224 has 24 divisors (see below), whose sum is σ = 39509190. Its totient is φ = 10188288.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721224 is 42212702.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 11222500 + 9498724 = 3350^2 + 3082^2 .

It is a junction number, because it is equal to n+sod(n) for n = 20721196 and 20721205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 35624 + ... + 36200.

Almost surely, 2^20721224 is an apocalyptic number.

It is an amenable number.

20721224 is a deficient number, since it is larger than the sum of its proper divisors (18787966).

20721224 is an equidigital number, since it uses as much as digits as its factorization.

20721224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 717 (or 646 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 20.

The square root of 20721224 is about 4552.0571173921. The cubic root of 20721224 is about 274.6661469288. Note that the first 3 decimals are identical.

Adding to 20721224 its reverse (42212702), we get a palindrome (62933926).

The spelling of 20721224 in words is "twenty million, seven hundred twenty-one thousand, two hundred twenty-four".