20812921 has 2 divisors, whose sum is σ = 20812922. Its totient is φ = 20812920.

The previous prime is 20812889. The next prime is 20812931. The reversal of 20812921 is 12921802.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 19321 = 4560^2 + 139^2 .

It is a cyclic number.

It is not a de Polignac number, because 20812921 - 2⁵ = 20812889 is a prime.

It is not a weakly prime, because it can be changed into another prime (20812931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10406460 + 10406461.

It is an arithmetic number, because the mean of its divisors is an integer number (10406461).

Almost surely, 2^20812921 is an apocalyptic number.

It is an amenable number.

20812921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20812921 is an equidigital number, since it uses as much as digits as its factorization.

20812921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 20812921 is about 4562.1180388061. The cubic root of 20812921 is about 275.0707079888.

Multiplying 20812921 by its sum of digits (25), we get a palindrome (520323025).

The spelling of 20812921 in words is "twenty million, eight hundred twelve thousand, nine hundred twenty-one".