645951 has 4 divisors (see below), whose sum is σ = 861272. Its totient is φ = 430632.

The previous prime is 645941. The next prime is 645973. The reversal of 645951 is 159546.

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

It is not a de Polignac number, because 645951 - 2¹⁴ = 629567 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645901) 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, 107656 + ... + 107661.

It is an arithmetic number, because the mean of its divisors is an integer number (215318).

2⁶⁴⁵⁹⁵¹ is an apocalyptic number.

645951 is a deficient number, since it is larger than the sum of its proper divisors (215321).

645951 is a wasteful number, since it uses less digits than its factorization.

645951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215320.

The product of its digits is 5400, while the sum is 30.

The square root of 645951 is about 803.7107688715. The cubic root of 645951 is about 86.4436689827.

It can be divided in two parts, 645 and 951, that added together give a triangular number (1596 = T₅₆).

The spelling of 645951 in words is "six hundred forty-five thousand, nine hundred fifty-one".