721657121 has 2 divisors, whose sum is σ = 721657122. Its totient is φ = 721657120.

The previous prime is 721657109. The next prime is 721657127. The reversal of 721657121 is 121756127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 713477521 + 8179600 = 26711^2 + 2860^2 .

It is a cyclic number.

It is not a de Polignac number, because 721657121 - 2¹⁴ = 721640737 is a prime.

It is not a weakly prime, because it can be changed into another prime (721657127) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360828560 + 360828561.

It is an arithmetic number, because the mean of its divisors is an integer number (360828561).

Almost surely, 2^721657121 is an apocalyptic number.

It is an amenable number.

721657121 is a deficient number, since it is larger than the sum of its proper divisors (1).

721657121 is an equidigital number, since it uses as much as digits as its factorization.

721657121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5880, while the sum is 32.

The square root of 721657121 is about 26863.6766098760. The cubic root of 721657121 is about 896.9680363384.

The spelling of 721657121 in words is "seven hundred twenty-one million, six hundred fifty-seven thousand, one hundred twenty-one".