21000018 has 16 divisors (see below), whose sum is σ = 45230976. Its totient is φ = 6461520.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000018 is 81000012.

It is a happy number.

21000018 is an esthetic number in base 9, because in such base its adjacent digits differ by 1.

It is an interprime number because it is at equal distance from previous prime (20999999) and next prime (21000037).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 20999967 and 21000012.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 134538 + ... + 134693.

It is an arithmetic number, because the mean of its divisors is an integer number (2826936).

Almost surely, 2^21000018 is an apocalyptic number.

21000018 is an abundant number, since it is smaller than the sum of its proper divisors (24230958).

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

21000018 is a wasteful number, since it uses less digits than its factorization.

21000018 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 269249.

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 21000018 is about 4582.5776589164. The cubic root of 21000018 is about 275.8924964645.

The spelling of 21000018 in words is "twenty-one million, eighteen", and thus it is an aban number and an uban number.