21315566 has 4 divisors (see below), whose sum is σ = 31973352. Its totient is φ = 10657782.

The previous prime is 21315563. The next prime is 21315571. The reversal of 21315566 is 66551312.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5328890 + ... + 5328893.

It is an arithmetic number, because the mean of its divisors is an integer number (7993338).

Almost surely, 2^21315566 is an apocalyptic number.

21315566 is a deficient number, since it is larger than the sum of its proper divisors (10657786).

21315566 is a wasteful number, since it uses less digits than its factorization.

21315566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10657785.

The product of its digits is 5400, while the sum is 29.

The square root of 21315566 is about 4616.8783826304. The cubic root of 21315566 is about 277.2674934749.

Adding to 21315566 its reverse (66551312), we get a palindrome (87866878).

The spelling of 21315566 in words is "twenty-one million, three hundred fifteen thousand, five hundred sixty-six".