721620657 has 60 divisors (see below), whose sum is σ = 1141545460. Its totient is φ = 453916224.

The previous prime is 721620643. The next prime is 721620689. The reversal of 721620657 is 756026127.

721620657 is a `hidden beast` number, since 7 + 21 + 620 + 6 + 5 + 7 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 581340321 + 140280336 = 24111^2 + 11844^2 .

It is not a de Polignac number, because 721620657 - 2⁶ = 721620593 is a prime.

It is a super-2 number, since 2×721620657² = 1041472745218223298, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721620637) 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 in 59 ways as a sum of consecutive naturals, for example, 6620319 + ... + 6620427.

Almost surely, 2^721620657 is an apocalyptic number.

It is an amenable number.

721620657 is a deficient number, since it is larger than the sum of its proper divisors (419924803).

721620657 is a wasteful number, since it uses less digits than its factorization.

721620657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 252 (or 196 counting only the distinct ones).

The product of its (nonzero) digits is 35280, while the sum is 36.

The square root of 721620657 is about 26862.9979153482. The cubic root of 721620657 is about 896.9529287052.

The spelling of 721620657 in words is "seven hundred twenty-one million, six hundred twenty thousand, six hundred fifty-seven".