21516566 has 4 divisors (see below), whose sum is σ = 32274852. Its totient is φ = 10758282.

The previous prime is 21516563. The next prime is 21516571. The reversal of 21516566 is 66561512.

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

It is a super-2 number, since 2×21516566² = 925925224864712, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21516563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5379140 + ... + 5379143.

It is an arithmetic number, because the mean of its divisors is an integer number (8068713).

Almost surely, 2^21516566 is an apocalyptic number.

21516566 is a deficient number, since it is larger than the sum of its proper divisors (10758286).

21516566 is a wasteful number, since it uses less digits than its factorization.

21516566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10758285.

The product of its digits is 10800, while the sum is 32.

The square root of 21516566 is about 4638.5952614989. The cubic root of 21516566 is about 278.1362874012.

The spelling of 21516566 in words is "twenty-one million, five hundred sixteen thousand, five hundred sixty-six".