21870018 has 24 divisors (see below), whose sum is σ = 47472048. Its totient is φ = 7276632.

The previous prime is 21870011. The next prime is 21870029. The reversal of 21870018 is 81007812.

It is a junction number, because it is equal to n+sod(n) for n = 21869973 and 21870000.

It is not an unprimeable number, because it can be changed into a prime (21870011) by changing a digit.

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 in 11 ways as a sum of consecutive naturals, for example, 16405 + ... + 17687.

It is an arithmetic number, because the mean of its divisors is an integer number (1978002).

Almost surely, 2^21870018 is an apocalyptic number.

21870018 is an abundant number, since it is smaller than the sum of its proper divisors (25602030).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21870018 is a wasteful number, since it uses less digits than its factorization.

21870018 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2238 (or 2235 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 21870018 is about 4676.5391049365. The cubic root of 21870018 is about 279.6510022576.

The spelling of 21870018 in words is "twenty-one million, eight hundred seventy thousand, eighteen".