21517838 has 4 divisors (see below), whose sum is σ = 32276760. Its totient is φ = 10758918.

The previous prime is 21517819. The next prime is 21517843. The reversal of 21517838 is 83871512.

It is a semiprime because it is the product of two primes.

It is a junction number, because it is equal to n+sod(n) for n = 21517798 and 21517807.

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, 5379458 + ... + 5379461.

It is an arithmetic number, because the mean of its divisors is an integer number (8069190).

Almost surely, 2^21517838 is an apocalyptic number.

21517838 is a deficient number, since it is larger than the sum of its proper divisors (10758922).

21517838 is a wasteful number, since it uses less digits than its factorization.

21517838 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10758921.

The product of its digits is 13440, while the sum is 35.

The square root of 21517838 is about 4638.7323699476. The cubic root of 21517838 is about 278.1417681764.

The spelling of 21517838 in words is "twenty-one million, five hundred seventeen thousand, eight hundred thirty-eight".