21538904 has 8 divisors (see below), whose sum is σ = 40385460. Its totient is φ = 10769448.

The previous prime is 21538903. The next prime is 21538939. The reversal of 21538904 is 40983512.

It is a tau number, because it is divible by the number of its divisors (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21538903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1346174 + ... + 1346189.

Almost surely, 2^21538904 is an apocalyptic number.

It is an amenable number.

21538904 is a deficient number, since it is larger than the sum of its proper divisors (18846556).

21538904 is a wasteful number, since it uses less digits than its factorization.

21538904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2692369 (or 2692365 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 32.

The square root of 21538904 is about 4641.0024779136. The cubic root of 21538904 is about 278.2325056602.

The spelling of 21538904 in words is "twenty-one million, five hundred thirty-eight thousand, nine hundred four".