1644963381 has 12 divisors (see below), whose sum is σ = 2479365408. Its totient is φ = 1048962024.

The previous prime is 1644963379. The next prime is 1644963443. The reversal of 1644963381 is 1833694461.

1644963381 is a `hidden beast` number, since 1 + 6 + 4 + 4 + 9 + 633 + 8 + 1 = 666.

It is not a de Polignac number, because 1644963381 - 2¹ = 1644963379 is a prime.

It is a super-3 number, since 3×1644963381³ (a number of 29 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1644963301) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3973135 + ... + 3973548.

It is an arithmetic number, because the mean of its divisors is an integer number (206613784).

Almost surely, 2^1644963381 is an apocalyptic number.

It is an amenable number.

1644963381 is a deficient number, since it is larger than the sum of its proper divisors (834402027).

1644963381 is a wasteful number, since it uses less digits than its factorization.

1644963381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7946712 (or 7946709 counting only the distinct ones).

The product of its digits is 373248, while the sum is 45.

The square root of 1644963381 is about 40558.1481455946. The cubic root of 1644963381 is about 1180.4621815368.

The spelling of 1644963381 in words is "one billion, six hundred forty-four million, nine hundred sixty-three thousand, three hundred eighty-one".