21555166 has 4 divisors (see below), whose sum is σ = 32332752. Its totient is φ = 10777582.

The previous prime is 21555113. The next prime is 21555179. The reversal of 21555166 is 66155512.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5388790 + ... + 5388793.

It is an arithmetic number, because the mean of its divisors is an integer number (8083188).

Almost surely, 2^21555166 is an apocalyptic number.

21555166 is a deficient number, since it is larger than the sum of its proper divisors (10777586).

21555166 is a wasteful number, since it uses less digits than its factorization.

21555166 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10777585.

The product of its digits is 9000, while the sum is 31.

The square root of 21555166 is about 4642.7541395168. The cubic root of 21555166 is about 278.3025104413.

The spelling of 21555166 in words is "twenty-one million, five hundred fifty-five thousand, one hundred sixty-six".