21221010100 has 72 divisors (see below), whose sum is σ = 46610563608. Its totient is φ = 8385331200.

The previous prime is 21221010077. The next prime is 21221010113. The reversal of 21221010100 is 101012212.

It can be written as a sum of positive squares in 12 ways, for example, as 60652944 + 21160357156 = 7788^2 + 145466^2 .

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6215994 + ... + 6219406.

It is an arithmetic number, because the mean of its divisors is an integer number (647368939).

Almost surely, 2^21221010100 is an apocalyptic number.

21221010100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21221010100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23305281804).

21221010100 is an abundant number, since it is smaller than the sum of its proper divisors (25389553508).

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

21221010100 is a wasteful number, since it uses less digits than its factorization.

21221010100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4165 (or 4158 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 10.

Adding to 21221010100 its reverse (101012212), we get a palindrome (21322022312).

The spelling of 21221010100 in words is "twenty-one billion, two hundred twenty-one million, ten thousand, one hundred".