21981206 has 8 divisors (see below), whose sum is σ = 35508144. Its totient is φ = 10145160.

The previous prime is 21981191. The next prime is 21981227. The reversal of 21981206 is 60218912.

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, 422690 + ... + 422741.

It is an arithmetic number, because the mean of its divisors is an integer number (4438518).

Almost surely, 2^21981206 is an apocalyptic number.

21981206 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

21981206 is a deficient number, since it is larger than the sum of its proper divisors (13526938).

21981206 is a wasteful number, since it uses less digits than its factorization.

21981206 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 845446.

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 21981206 is about 4688.4118846364. The cubic root of 21981206 is about 280.1241201412.

The spelling of 21981206 in words is "twenty-one million, nine hundred eighty-one thousand, two hundred six".