646240021 has 4 divisors (see below), whose sum is σ = 738560032. Its totient is φ = 553920012.

The previous prime is 646240009. The next prime is 646240033. The reversal of 646240021 is 120042646.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (646240009) and next prime (646240033).

It is a cyclic number.

It is not a de Polignac number, because 646240021 - 2¹⁵ = 646207253 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646240081) 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, 46159995 + ... + 46160008.

It is an arithmetic number, because the mean of its divisors is an integer number (184640008).

Almost surely, 2^646240021 is an apocalyptic number.

It is an amenable number.

646240021 is a deficient number, since it is larger than the sum of its proper divisors (92320011).

646240021 is an equidigital number, since it uses as much as digits as its factorization.

646240021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92320010.

The product of its (nonzero) digits is 2304, while the sum is 25.

The square root of 646240021 is about 25421.2513657373. The cubic root of 646240021 is about 864.5655969750.

Adding to 646240021 its reverse (120042646), we get a palindrome (766282667).

The spelling of 646240021 in words is "six hundred forty-six million, two hundred forty thousand, twenty-one".