21121221100 has 72 divisors (see below), whose sum is σ = 52499639808. Its totient is φ = 7225108800.

The previous prime is 21121221083. The next prime is 21121221113. The reversal of 21121221100 is 112212112.

21121221100 = T₁₅₄₄₉ + T₁₅₄₅₀ + ... + T₁₅₆₂₃.

It is a super-2 number, since 2×21121221100² (a number of 21 digits) contains 22 as substring.

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, 276045 + ... + 344155.

It is an arithmetic number, because the mean of its divisors is an integer number (729161664).

Almost surely, 2^21121221100 is an apocalyptic number.

21121221100 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 21121221100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26249819904).

21121221100 is an abundant number, since it is smaller than the sum of its proper divisors (31378418708).

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

21121221100 is a wasteful number, since it uses less digits than its factorization.

21121221100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 68575 (or 68568 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 13.

Adding to 21121221100 its reverse (112212112), we get a palindrome (21233433212).

The spelling of 21121221100 in words is "twenty-one billion, one hundred twenty-one million, two hundred twenty-one thousand, one hundred".