21420018 has 16 divisors (see below), whose sum is σ = 47600160. Its totient is φ = 7139988.

The previous prime is 21420013. The next prime is 21420023. The reversal of 21420018 is 81002412.

It is an interprime number because it is at equal distance from previous prime (21420013) and next prime (21420023).

It is a super-2 number, since 2×21420018² = 917634342240648, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21420013) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 198280 + ... + 198387.

It is an arithmetic number, because the mean of its divisors is an integer number (2975010).

Almost surely, 2^21420018 is an apocalyptic number.

21420018 is an abundant number, since it is smaller than the sum of its proper divisors (26180142).

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

21420018 is a wasteful number, since it uses less digits than its factorization.

21420018 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 396678 (or 396672 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21420018 is about 4628.1765307732. The cubic root of 21420018 is about 277.7196507825.

The spelling of 21420018 in words is "twenty-one million, four hundred twenty thousand, eighteen".