21001021220 has 12 divisors (see below), whose sum is σ = 44102144604. Its totient is φ = 8400408480.

The previous prime is 21001021219. The next prime is 21001021229. The reversal of 21001021220 is 2212010012.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 16287374884 + 4713646336 = 127622^2 + 68656^2 .

It is not an unprimeable number, because it can be changed into a prime (21001021229) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 525025511 + ... + 525025550.

It is an arithmetic number, because the mean of its divisors is an integer number (3675178717).

Almost surely, 2^21001021220 is an apocalyptic number.

21001021220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001021220 is an abundant number, since it is smaller than the sum of its proper divisors (23101123384).

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

21001021220 is a wasteful number, since it uses less digits than its factorization.

21001021220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1050051070 (or 1050051068 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21001021220 its reverse (2212010012), we get a palindrome (23213031232).

The spelling of 21001021220 in words is "twenty-one billion, one million, twenty-one thousand, two hundred twenty".