19725721 has 4 divisors (see below), whose sum is σ = 19736244. Its totient is φ = 19715200.

The previous prime is 19725701. The next prime is 19725731. The reversal of 19725721 is 12752791.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12752791 = 59 ⋅216149.

It can be written as a sum of positive squares in 2 ways, for example, as 4044121 + 15681600 = 2011^2 + 3960^2 .

It is a cyclic number.

It is not a de Polignac number, because 19725721 - 2⁵ = 19725689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19725701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1600 + ... + 6481.

It is an arithmetic number, because the mean of its divisors is an integer number (4934061).

Almost surely, 2^19725721 is an apocalyptic number.

It is an amenable number.

19725721 is a deficient number, since it is larger than the sum of its proper divisors (10523).

19725721 is an equidigital number, since it uses as much as digits as its factorization.

19725721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10522.

The product of its digits is 8820, while the sum is 34.

The square root of 19725721 is about 4441.3647677262. The cubic root of 19725721 is about 270.1951994936.

The spelling of 19725721 in words is "nineteen million, seven hundred twenty-five thousand, seven hundred twenty-one".