645421 has 4 divisors (see below), whose sum is σ = 737632. Its totient is φ = 553212.

The previous prime is 645419. The next prime is 645431. The reversal of 645421 is 124546.

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 an emirpimes, since its reverse is a distinct semiprime: 124546 = 2 ⋅62273.

It is a cyclic number.

It is not a de Polignac number, because 645421 - 2¹ = 645419 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 645392 and 645401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645431) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46095 + ... + 46108.

It is an arithmetic number, because the mean of its divisors is an integer number (184408).

2⁶⁴⁵⁴²¹ is an apocalyptic number.

It is an amenable number.

645421 is a deficient number, since it is larger than the sum of its proper divisors (92211).

645421 is an equidigital number, since it uses as much as digits as its factorization.

645421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92210.

The product of its digits is 960, while the sum is 22.

The square root of 645421 is about 803.3809806063. The cubic root of 645421 is about 86.4200202949.

Adding to 645421 its reverse (124546), we get a palindrome (769967).

The spelling of 645421 in words is "six hundred forty-five thousand, four hundred twenty-one".