640401021 has 24 divisors (see below), whose sum is σ = 1019354336. Its totient is φ = 384924960.

The previous prime is 640401011. The next prime is 640401031. The reversal of 640401021 is 120104046.

640401021 is a `hidden beast` number, since 640 + 4 + 0 + 1 + 0 + 21 = 666.

It is an interprime number because it is at equal distance from previous prime (640401011) and next prime (640401031).

It is not a de Polignac number, because 640401021 - 2¹³ = 640392829 is a prime.

It is a super-2 number, since 2×640401021² = 820226935395684882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 640400985 and 640401003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640401001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 58615 + ... + 68676.

Almost surely, 2^640401021 is an apocalyptic number.

It is an amenable number.

640401021 is a deficient number, since it is larger than the sum of its proper divisors (378953315).

640401021 is a wasteful number, since it uses less digits than its factorization.

640401021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127353 (or 127350 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 640401021 is about 25306.1459135918. The cubic root of 640401021 is about 861.9538329216.

Adding to 640401021 its reverse (120104046), we get a palindrome (760505067).

The spelling of 640401021 in words is "six hundred forty million, four hundred one thousand, twenty-one".