21001572 has 48 divisors (see below), whose sum is σ = 54828480. Its totient is φ = 6951744.

The previous prime is 21001559. The next prime is 21001577. The reversal of 21001572 is 27510012.

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 (21001577) 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, 17008 + ... + 18200.

It is an arithmetic number, because the mean of its divisors is an integer number (1142260).

Almost surely, 2^21001572 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001572, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27414240).

21001572 is an abundant number, since it is smaller than the sum of its proper divisors (33826908).

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

21001572 is a wasteful number, since it uses less digits than its factorization.

21001572 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1369 (or 1361 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 21001572 is about 4582.7472110078. The cubic root of 21001572 is about 275.8993016390.

Adding to 21001572 its reverse (27510012), we get a palindrome (48511584).

The spelling of 21001572 in words is "twenty-one million, one thousand, five hundred seventy-two".