21993424 has 10 divisors (see below), whose sum is σ = 42612290. Its totient is φ = 10996704.

The previous prime is 21993409. The next prime is 21993437. The reversal of 21993424 is 42439912.

It can be written as a sum of positive squares in only one way, i.e., 13927824 + 8065600 = 3732^2 + 2840^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21993424.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 687279 + ... + 687310.

It is an arithmetic number, because the mean of its divisors is an integer number (4261229).

Almost surely, 2^21993424 is an apocalyptic number.

It is an amenable number.

21993424 is a deficient number, since it is larger than the sum of its proper divisors (20618866).

21993424 is a wasteful number, since it uses less digits than its factorization.

21993424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1374597 (or 1374591 counting only the distinct ones).

The product of its digits is 15552, while the sum is 34.

The square root of 21993424 is about 4689.7147034761. The cubic root of 21993424 is about 280.1760117824.

The spelling of 21993424 in words is "twenty-one million, nine hundred ninety-three thousand, four hundred twenty-four".