646656021 has 32 divisors (see below), whose sum is σ = 1064845440. Its totient is φ = 384508800.

The previous prime is 646656019. The next prime is 646656037. The reversal of 646656021 is 120656646.

It is a happy number.

646656021 is a `hidden beast` number, since 6 + 46 + 6 + 5 + 602 + 1 = 666.

It is not a de Polignac number, because 646656021 - 2¹ = 646656019 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646656091) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4800 + ... + 36281.

It is an arithmetic number, because the mean of its divisors is an integer number (33276420).

Almost surely, 2^646656021 is an apocalyptic number.

It is an amenable number.

646656021 is a deficient number, since it is larger than the sum of its proper divisors (418189419).

646656021 is a wasteful number, since it uses less digits than its factorization.

646656021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41154 (or 41148 counting only the distinct ones).

The product of its (nonzero) digits is 51840, while the sum is 36.

The square root of 646656021 is about 25429.4321800547. The cubic root of 646656021 is about 864.7510709633.

The spelling of 646656021 in words is "six hundred forty-six million, six hundred fifty-six thousand, twenty-one".