21081856 has 18 divisors (see below), whose sum is σ = 42081872. Its totient is φ = 10540800.

The previous prime is 21081833. The next prime is 21081857. The reversal of 21081856 is 65818012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081857) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40920 + ... + 41431.

Almost surely, 2^21081856 is an apocalyptic number.

It is an amenable number.

21081856 is a deficient number, since it is larger than the sum of its proper divisors (21000016).

21081856 is an frugal number, since it uses more digits than its factorization.

21081856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82367 (or 82353 counting only the distinct ones).

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

The square root of 21081856 is about 4591.4982304254. The cubic root of 21081856 is about 276.2504203429.

Adding to 21081856 its reverse (65818012), we get a palindrome (86899868).

The spelling of 21081856 in words is "twenty-one million, eighty-one thousand, eight hundred fifty-six".