21881644 has 6 divisors (see below), whose sum is σ = 38292884. Its totient is φ = 10940820.

The previous prime is 21881627. The next prime is 21881647. The reversal of 21881644 is 44618812.

It is not an unprimeable number, because it can be changed into a prime (21881647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2735202 + ... + 2735209.

Almost surely, 2^21881644 is an apocalyptic number.

It is an amenable number.

21881644 is a deficient number, since it is larger than the sum of its proper divisors (16411240).

21881644 is a wasteful number, since it uses less digits than its factorization.

21881644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5470415 (or 5470413 counting only the distinct ones).

The product of its digits is 12288, while the sum is 34.

The square root of 21881644 is about 4677.7819530200. The cubic root of 21881644 is about 279.7005472040.

The spelling of 21881644 in words is "twenty-one million, eight hundred eighty-one thousand, six hundred forty-four".