20240721 has 6 divisors (see below), whose sum is σ = 29236610. Its totient is φ = 13493808.

The previous prime is 20240683. The next prime is 20240723. The reversal of 20240721 is 12704202.

It can be written as a sum of positive squares in only one way, i.e., 17139600 + 3101121 = 4140^2 + 1761^2 .

It is not a de Polignac number, because 20240721 - 2¹⁵ = 20207953 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20240694 and 20240703.

It is not an unprimeable number, because it can be changed into a prime (20240723) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1124476 + ... + 1124493.

Almost surely, 2^20240721 is an apocalyptic number.

It is an amenable number.

20240721 is a deficient number, since it is larger than the sum of its proper divisors (8995889).

20240721 is a wasteful number, since it uses less digits than its factorization.

20240721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2248975 (or 2248972 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 18.

The square root of 20240721 is about 4498.9688818662. The cubic root of 20240721 is about 272.5264503125.

Subtracting from 20240721 its sum of digits (18), we obtain a triangular number (20240703 = T₆₃₆₂).

Adding to 20240721 its reverse (12704202), we get a palindrome (32944923).

The spelling of 20240721 in words is "twenty million, two hundred forty thousand, seven hundred twenty-one".