21001530 has 64 divisors (see below), whose sum is σ = 57397248. Its totient is φ = 4868160.

The previous prime is 21001529. The next prime is 21001531. The reversal of 21001530 is 3510012.

It is an interprime number because it is at equal distance from previous prime (21001529) and next prime (21001531).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21001531) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 6207 + ... + 8973.

It is an arithmetic number, because the mean of its divisors is an integer number (896832).

Almost surely, 2^21001530 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001530, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28698624).

21001530 is an abundant number, since it is smaller than the sum of its proper divisors (36395718).

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

21001530 is a wasteful number, since it uses less digits than its factorization.

21001530 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2811.

The product of its (nonzero) digits is 30, while the sum is 12.

The square root of 21001530 is about 4582.7426286013. The cubic root of 21001530 is about 275.8991177198.

Adding to 21001530 its reverse (3510012), we get a palindrome (24511542).

The spelling of 21001530 in words is "twenty-one million, one thousand, five hundred thirty".