645901819 has 4 divisors (see below), whose sum is σ = 646518600. Its totient is φ = 645285040.

The previous prime is 645901813. The next prime is 645901829. The reversal of 645901819 is 918109546.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 645901819 - 2³ = 645901811 is a prime.

It is a super-2 number, since 2×645901819² = 834378319575017522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (645901811) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 306817 + ... + 308914.

It is an arithmetic number, because the mean of its divisors is an integer number (161629650).

Almost surely, 2^645901819 is an apocalyptic number.

645901819 is a deficient number, since it is larger than the sum of its proper divisors (616781).

645901819 is a wasteful number, since it uses less digits than its factorization.

645901819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 616780.

The product of its (nonzero) digits is 77760, while the sum is 43.

The square root of 645901819 is about 25414.5985409961. The cubic root of 645901819 is about 864.4147506295.

The spelling of 645901819 in words is "six hundred forty-five million, nine hundred one thousand, eight hundred nineteen".