640420621 has 2 divisors, whose sum is σ = 640420622. Its totient is φ = 640420620.

The previous prime is 640420619. The next prime is 640420673. The reversal of 640420621 is 126024046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 603684900 + 36735721 = 24570^2 + 6061^2 .

It is a cyclic number.

It is not a de Polignac number, because 640420621 - 2¹ = 640420619 is a prime.

Together with 640420619, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640420691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320210310 + 320210311.

It is an arithmetic number, because the mean of its divisors is an integer number (320210311).

Almost surely, 2^640420621 is an apocalyptic number.

It is an amenable number.

640420621 is a deficient number, since it is larger than the sum of its proper divisors (1).

640420621 is an equidigital number, since it uses as much as digits as its factorization.

640420621 is an evil number, because the sum of its binary digits is even.

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

The square root of 640420621 is about 25306.5331683342. The cubic root of 640420621 is about 861.9626264340.

Adding to 640420621 its reverse (126024046), we get a palindrome (766444667).

The spelling of 640420621 in words is "six hundred forty million, four hundred twenty thousand, six hundred twenty-one".