640206021 has 48 divisors (see below), whose sum is σ = 1095571008. Its totient is φ = 329414400.

The previous prime is 640206011. The next prime is 640206071. The reversal of 640206021 is 120602046.

It is a happy number.

It is not a de Polignac number, because 640206021 - 2⁶ = 640205957 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640206011) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 74266 + ... + 82436.

It is an arithmetic number, because the mean of its divisors is an integer number (22824396).

Almost surely, 2^640206021 is an apocalyptic number.

It is an amenable number.

640206021 is a deficient number, since it is larger than the sum of its proper divisors (455364987).

640206021 is a wasteful number, since it uses less digits than its factorization.

640206021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8242 (or 8235 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 21.

The square root of 640206021 is about 25302.2928012463. The cubic root of 640206021 is about 861.8663366733.

Adding to 640206021 its reverse (120602046), we get a palindrome (760808067).

The spelling of 640206021 in words is "six hundred forty million, two hundred six thousand, twenty-one".