21155806 has 8 divisors (see below), whose sum is σ = 36267120. Its totient is φ = 9066768.

The previous prime is 21155789. The next prime is 21155839. The reversal of 21155806 is 60855112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 755551 + ... + 755578.

It is an arithmetic number, because the mean of its divisors is an integer number (4533390).

Almost surely, 2^21155806 is an apocalyptic number.

21155806 is a deficient number, since it is larger than the sum of its proper divisors (15111314).

21155806 is a wasteful number, since it uses less digits than its factorization.

21155806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1511138.

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 21155806 is about 4599.5441078437. The cubic root of 21155806 is about 276.5730497279.

It can be divided in two parts, 2115 and 5806, that added together give a square (7921 = 89²).

The spelling of 21155806 in words is "twenty-one million, one hundred fifty-five thousand, eight hundred six".