644649281 has 8 divisors (see below), whose sum is σ = 666326400. Its totient is φ = 623330640.

The previous prime is 644649263. The next prime is 644649287. The reversal of 644649281 is 182946446.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644649281 - 2²² = 640454977 is a prime.

It is a super-2 number, since 2×644649281² = 831145390987633922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644649287) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 85961 + ... + 93158.

It is an arithmetic number, because the mean of its divisors is an integer number (83290800).

Almost surely, 2^644649281 is an apocalyptic number.

644649281 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

644649281 is a deficient number, since it is larger than the sum of its proper divisors (21677119).

644649281 is a wasteful number, since it uses less digits than its factorization.

644649281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179239.

The product of its digits is 331776, while the sum is 44.

The square root of 644649281 is about 25389.9444859574. The cubic root of 644649281 is about 863.8556290447.

The spelling of 644649281 in words is "six hundred forty-four million, six hundred forty-nine thousand, two hundred eighty-one".