721905421 has 4 divisors (see below), whose sum is σ = 735526332. Its totient is φ = 708284512.

The previous prime is 721905403. The next prime is 721905427. The reversal of 721905421 is 124509127.

721905421 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 247275625 + 474629796 = 15725^2 + 21786^2 .

It is a cyclic number.

It is not a de Polignac number, because 721905421 - 2¹⁷ = 721774349 is a prime.

It is a super-2 number, since 2×721905421² = 1042294873738374482, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721905427) 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, 6810376 + ... + 6810481.

It is an arithmetic number, because the mean of its divisors is an integer number (183881583).

Almost surely, 2^721905421 is an apocalyptic number.

It is an amenable number.

721905421 is a deficient number, since it is larger than the sum of its proper divisors (13620911).

721905421 is a wasteful number, since it uses less digits than its factorization.

721905421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13620910.

The product of its (nonzero) digits is 5040, while the sum is 31.

The square root of 721905421 is about 26868.2976944949. The cubic root of 721905421 is about 897.0708975720.

The spelling of 721905421 in words is "seven hundred twenty-one million, nine hundred five thousand, four hundred twenty-one".