20824721 has 2 divisors, whose sum is σ = 20824722. Its totient is φ = 20824720.

The previous prime is 20824693. The next prime is 20824757. The reversal of 20824721 is 12742802.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14250625 + 6574096 = 3775^2 + 2564^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20824721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20824781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10412360 + 10412361.

It is an arithmetic number, because the mean of its divisors is an integer number (10412361).

Almost surely, 2^20824721 is an apocalyptic number.

It is an amenable number.

20824721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20824721 is an equidigital number, since it uses as much as digits as its factorization.

20824721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 20824721 is about 4563.4111145063. The cubic root of 20824721 is about 275.1226824511.

The spelling of 20824721 in words is "twenty million, eight hundred twenty-four thousand, seven hundred twenty-one".