21001518 has 48 divisors (see below), whose sum is σ = 47873280. Its totient is φ = 6899256.

The previous prime is 21001493. The next prime is 21001523. The reversal of 21001518 is 81510012.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21001518.

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 23 ways as a sum of consecutive naturals, for example, 38121 + ... + 38667.

It is an arithmetic number, because the mean of its divisors is an integer number (997360).

Almost surely, 2^21001518 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001518, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23936640).

21001518 is an abundant number, since it is smaller than the sum of its proper divisors (26871762).

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

21001518 is an equidigital number, since it uses as much as digits as its factorization.

21001518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 643 (or 631 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21001518 is about 4582.7413193415. The cubic root of 21001518 is about 275.8990651714.

The spelling of 21001518 in words is "twenty-one million, one thousand, five hundred eighteen".