21085816 has 8 divisors (see below), whose sum is σ = 39535920. Its totient is φ = 10542904.

The previous prime is 21085789. The next prime is 21085837. The reversal of 21085816 is 61858012.

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

It is a super-2 number, since 2×21085816² = 889223272771712, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1317856 + ... + 1317871.

It is an arithmetic number, because the mean of its divisors is an integer number (4941990).

Almost surely, 2^21085816 is an apocalyptic number.

It is an amenable number.

21085816 is a deficient number, since it is larger than the sum of its proper divisors (18450104).

21085816 is a wasteful number, since it uses less digits than its factorization.

21085816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2635733 (or 2635729 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 31.

The square root of 21085816 is about 4591.9294419666. The cubic root of 21085816 is about 276.2677161505.

The spelling of 21085816 in words is "twenty-one million, eighty-five thousand, eight hundred sixteen".