644216281 has 4 divisors (see below), whose sum is σ = 650470912. Its totient is φ = 637961652.

The previous prime is 644216249. The next prime is 644216297. The reversal of 644216281 is 182612446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 182612446 = 2 ⋅91306223.

It is a cyclic number.

It is not a de Polignac number, because 644216281 - 2⁵ = 644216249 is a prime.

It is a super-2 number, since 2×644216281² = 830029233410941922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644216381) 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, 3127161 + ... + 3127366.

It is an arithmetic number, because the mean of its divisors is an integer number (162617728).

Almost surely, 2^644216281 is an apocalyptic number.

It is an amenable number.

644216281 is a deficient number, since it is larger than the sum of its proper divisors (6254631).

644216281 is a wasteful number, since it uses less digits than its factorization.

644216281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6254630.

The product of its digits is 18432, while the sum is 34.

The square root of 644216281 is about 25381.4160558468. The cubic root of 644216281 is about 863.6621733279.

The spelling of 644216281 in words is "six hundred forty-four million, two hundred sixteen thousand, two hundred eighty-one".