21509138 has 24 divisors (see below), whose sum is σ = 37825200. Its totient is φ = 9146088.

The previous prime is 21509119. The next prime is 21509141. The reversal of 21509138 is 83190512.

It is a self number, because there is not a number n which added to its sum of digits gives 21509138.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 12833 + ... + 14411.

It is an arithmetic number, because the mean of its divisors is an integer number (1576050).

Almost surely, 2^21509138 is an apocalyptic number.

21509138 is a deficient number, since it is larger than the sum of its proper divisors (16316062).

21509138 is a wasteful number, since it uses less digits than its factorization.

21509138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1734 (or 1727 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 21509138 is about 4637.7945189497. The cubic root of 21509138 is about 278.1042774275.

The spelling of 21509138 in words is "twenty-one million, five hundred nine thousand, one hundred thirty-eight".