21021066 has 64 divisors (see below), whose sum is σ = 52208640. Its totient is φ = 6214320.

The previous prime is 21021053. The next prime is 21021067. The reversal of 21021066 is 66012012.

It is a happy number.

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 (21021067) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25131 + ... + 25953.

It is an arithmetic number, because the mean of its divisors is an integer number (815760).

Almost surely, 2^21021066 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21021066, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26104320).

21021066 is an abundant number, since it is smaller than the sum of its proper divisors (31187574).

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

21021066 is a wasteful number, since it uses less digits than its factorization.

21021066 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 888 (or 882 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21021066 is about 4584.8736078544. The cubic root of 21021066 is about 275.9846399770.

Adding to 21021066 its reverse (66012012), we get a palindrome (87033078).

It can be divided in two parts, 210210 and 66, that added together give a triangular number (210276 = T₆₄₈).

The spelling of 21021066 in words is "twenty-one million, twenty-one thousand, sixty-six".