21001002012 has 72 divisors (see below), whose sum is σ = 55510640640. Its totient is φ = 6681866400.

The previous prime is 21001001971. The next prime is 21001002019. The reversal of 21001002012 is 21020010012.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21001001985 and 21001002003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001002019) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 370137 + ... + 423087.

It is an arithmetic number, because the mean of its divisors is an integer number (770981120).

Almost surely, 2^21001002012 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 21001002012, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27755320320).

21001002012 is an abundant number, since it is smaller than the sum of its proper divisors (34509638628).

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

21001002012 is a wasteful number, since it uses less digits than its factorization.

21001002012 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53463 (or 53458 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

Adding to 21001002012 its reverse (21020010012), we get a palindrome (42021012024).

The spelling of 21001002012 in words is "twenty-one billion, one million, two thousand, twelve".