21006918 has 32 divisors (see below), whose sum is σ = 47330400. Its totient is φ = 6906384.

The previous prime is 21006907. The next prime is 21006941. The reversal of 21006918 is 81960012.

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 = 21006891 and 21006900.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 287730 + ... + 287802.

It is an arithmetic number, because the mean of its divisors is an integer number (1479075).

Almost surely, 2^21006918 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21006918, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23665200).

21006918 is an abundant number, since it is smaller than the sum of its proper divisors (26323482).

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

21006918 is an frugal number, since it uses more digits than its factorization.

21006918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 230 (or 78 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 21006918 is about 4583.3304484839. The cubic root of 21006918 is about 275.9227099270.

Multiplying 21006918 by its product of nonzero digits (864), we get a cube (18149977152 = 2628³).

The spelling of 21006918 in words is "twenty-one million, six thousand, nine hundred eighteen".