21090618 has 40 divisors (see below), whose sum is σ = 47763540. Its totient is φ = 6955200.

The previous prime is 21090583. The next prime is 21090631. The reversal of 21090618 is 81609012.

It can be written as a sum of positive squares in 2 ways, for example, as 16916769 + 4173849 = 4113^2 + 2043^2 .

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

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 = 21090591 and 21090600.

It is a congruent number.

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 19 ways as a sum of consecutive naturals, for example, 15718 + ... + 17006.

Almost surely, 2^21090618 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21090618, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23881770).

21090618 is an abundant number, since it is smaller than the sum of its proper divisors (26672922).

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

21090618 is a wasteful number, since it uses less digits than its factorization.

21090618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1404 (or 1395 counting only the distinct ones).

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

The square root of 21090618 is about 4592.4522860886. The cubic root of 21090618 is about 276.2886865962.

The spelling of 21090618 in words is "twenty-one million, ninety thousand, six hundred eighteen".