21001021206 has 128 divisors (see below), whose sum is σ = 47891644416. Its totient is φ = 6084046080.

The previous prime is 21001021187. The next prime is 21001021219. The reversal of 21001021206 is 60212010012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 34597755 + ... + 34598361.

It is an arithmetic number, because the mean of its divisors is an integer number (374153472).

Almost surely, 2^21001021206 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21001021206, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23945822208).

21001021206 is an abundant number, since it is smaller than the sum of its proper divisors (26890623210).

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

21001021206 is a wasteful number, since it uses less digits than its factorization.

21001021206 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 906.

The product of its (nonzero) digits is 48, while the sum is 15.

Adding to 21001021206 its reverse (60212010012), we get a palindrome (81213031218).

The spelling of 21001021206 in words is "twenty-one billion, one million, twenty-one thousand, two hundred six".