645631 has 4 divisors (see below), whose sum is σ = 737872. Its totient is φ = 553392.

The previous prime is 645629. The next prime is 645641. The reversal of 645631 is 136546.

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

It is not a de Polignac number, because 645631 - 2¹ = 645629 is a prime.

It is a super-2 number, since 2×645631² = 833678776322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 645596 and 645605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645611) 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, 46110 + ... + 46123.

It is an arithmetic number, because the mean of its divisors is an integer number (184468).

2⁶⁴⁵⁶³¹ is an apocalyptic number.

645631 is a deficient number, since it is larger than the sum of its proper divisors (92241).

645631 is an equidigital number, since it uses as much as digits as its factorization.

645631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92240.

The product of its digits is 2160, while the sum is 25.

The square root of 645631 is about 803.5116676191. The cubic root of 645631 is about 86.4293920777.

The spelling of 645631 in words is "six hundred forty-five thousand, six hundred thirty-one".