644956 has 24 divisors (see below), whose sum is σ = 1238720. Its totient is φ = 292032.

The previous prime is 644951. The next prime is 644977. The reversal of 644956 is 659446.

644956 = T₁ + T₂ + ... + T₁₅₆.

644956 is a nontrivial binomial coefficient, being equal to C(158, 3).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644951) by changing a digit.

644956 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is the 156-th tetrahedral number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4030 + ... + 4186.

2⁶⁴⁴⁹⁵⁶ is an apocalyptic number.

It is an amenable number.

644956 is a deficient number, since it is larger than the sum of its proper divisors (593764).

644956 is a wasteful number, since it uses less digits than its factorization.

644956 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 253 (or 251 counting only the distinct ones).

The product of its digits is 25920, while the sum is 34.

The square root of 644956 is about 803.0915265398. The cubic root of 644956 is about 86.3992612534.

It can be divided in two parts, 644 and 956, that added together give a square (1600 = 40²).

The spelling of 644956 in words is "six hundred forty-four thousand, nine hundred fifty-six".