21717018 has 32 divisors (see below), whose sum is σ = 48700800. Its totient is φ = 7172928.

The previous prime is 21717013. The next prime is 21717029. The reversal of 21717018 is 81071712.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 21716982 and 21717000.

It is not an unprimeable number, because it can be changed into a prime (21717013) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4323 + ... + 7881.

It is an arithmetic number, because the mean of its divisors is an integer number (1521900).

Almost surely, 2^21717018 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21717018, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24350400).

21717018 is an abundant number, since it is smaller than the sum of its proper divisors (26983782).

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

21717018 is a wasteful number, since it uses less digits than its factorization.

21717018 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3683 (or 3677 counting only the distinct ones).

The product of its (nonzero) digits is 784, while the sum is 27.

The square root of 21717018 is about 4660.1521434391. The cubic root of 21717018 is about 278.9973407077.

The spelling of 21717018 in words is "twenty-one million, seven hundred seventeen thousand, eighteen".