721045309 has 4 divisors (see below), whose sum is σ = 730922716. Its totient is φ = 711167904.

The previous prime is 721045291. The next prime is 721045417. The reversal of 721045309 is 903540127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 903540127 = 7 ⋅129077161.

It can be written as a sum of positive squares in 2 ways, for example, as 375196900 + 345848409 = 19370^2 + 18597^2 .

It is a cyclic number.

It is not a de Polignac number, because 721045309 - 2¹³ = 721037117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721045109) 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, 4938594 + ... + 4938739.

It is an arithmetic number, because the mean of its divisors is an integer number (182730679).

Almost surely, 2^721045309 is an apocalyptic number.

It is an amenable number.

721045309 is a deficient number, since it is larger than the sum of its proper divisors (9877407).

721045309 is an equidigital number, since it uses as much as digits as its factorization.

721045309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9877406.

The product of its (nonzero) digits is 7560, while the sum is 31.

The square root of 721045309 is about 26852.2868486094. The cubic root of 721045309 is about 896.7144851957.

The spelling of 721045309 in words is "seven hundred twenty-one million, forty-five thousand, three hundred nine".