645490 has 16 divisors (see below), whose sum is σ = 1230552. Its totient is φ = 242944.

The previous prime is 645481. The next prime is 645493. The reversal of 645490 is 94546.

645490 = T₂₄₄ + T₂₄₅ + ... + T₂₆₃.

It can be written as a sum of positive squares in 4 ways, for example, as 408321 + 237169 = 639^2 + 487^2 .

It is not an unprimeable number, because it can be changed into a prime (645493) 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 7 ways as a sum of consecutive naturals, for example, 1729 + ... + 2068.

2⁶⁴⁵⁴⁹⁰ is an apocalyptic number.

645490 is a deficient number, since it is larger than the sum of its proper divisors (585062).

645490 is a wasteful number, since it uses less digits than its factorization.

645490 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3821.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 645490 is about 803.4239229697. The cubic root of 645490 is about 86.4230998192.

The spelling of 645490 in words is "six hundred forty-five thousand, four hundred ninety".