645040421 has 4 divisors (see below), whose sum is σ = 645100032. Its totient is φ = 644980812.

The previous prime is 645040411. The next prime is 645040447. The reversal of 645040421 is 124040546.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645040421 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645040411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8495 + ... + 36908.

It is an arithmetic number, because the mean of its divisors is an integer number (161275008).

Almost surely, 2^645040421 is an apocalyptic number.

It is an amenable number.

645040421 is a deficient number, since it is larger than the sum of its proper divisors (59611).

645040421 is a wasteful number, since it uses less digits than its factorization.

645040421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59610.

The product of its (nonzero) digits is 3840, while the sum is 26.

The square root of 645040421 is about 25397.6459735937. The cubic root of 645040421 is about 864.0303080968.

Adding to 645040421 its reverse (124040546), we get a palindrome (769080967).

The spelling of 645040421 in words is "six hundred forty-five million, forty thousand, four hundred twenty-one".