20436721 has 2 divisors, whose sum is σ = 20436722. Its totient is φ = 20436720.

The previous prime is 20436707. The next prime is 20436733. The reversal of 20436721 is 12763402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10758400 + 9678321 = 3280^2 + 3111^2 .

It is a cyclic number.

It is not a de Polignac number, because 20436721 - 2⁷ = 20436593 is a prime.

It is not a weakly prime, because it can be changed into another prime (20436751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10218360 + 10218361.

It is an arithmetic number, because the mean of its divisors is an integer number (10218361).

Almost surely, 2^20436721 is an apocalyptic number.

It is an amenable number.

20436721 is a deficient number, since it is larger than the sum of its proper divisors (1).

20436721 is an equidigital number, since it uses as much as digits as its factorization.

20436721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 25.

The square root of 20436721 is about 4520.6991715884. The cubic root of 20436721 is about 273.4032914658.

The spelling of 20436721 in words is "twenty million, four hundred thirty-six thousand, seven hundred twenty-one".