640696421 has 2 divisors, whose sum is σ = 640696422. Its totient is φ = 640696420.

The previous prime is 640696409. The next prime is 640696423. The reversal of 640696421 is 124696046.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 635745796 + 4950625 = 25214^2 + 2225^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640696421 is a prime.

Together with 640696423, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640696423) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320348210 + 320348211.

It is an arithmetic number, because the mean of its divisors is an integer number (320348211).

Almost surely, 2^640696421 is an apocalyptic number.

It is an amenable number.

640696421 is a deficient number, since it is larger than the sum of its proper divisors (1).

640696421 is an equidigital number, since it uses as much as digits as its factorization.

640696421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 62208, while the sum is 38.

The square root of 640696421 is about 25311.9817675345. The cubic root of 640696421 is about 862.0863446937.

The spelling of 640696421 in words is "six hundred forty million, six hundred ninety-six thousand, four hundred twenty-one".