21111212100 has 216 divisors, whose sum is σ = 68498928288. Its totient is φ = 4978483200.

The previous prime is 21111212077. The next prime is 21111212123. The reversal of 21111212100 is 121211112.

It is an interprime number because it is at equal distance from previous prime (21111212077) and next prime (21111212123).

It is a Harshad number since it is a multiple of its sum of digits (12).

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 4515364 + ... + 4520036.

It is an arithmetic number, because the mean of its divisors is an integer number (317124668).

Almost surely, 2^21111212100 is an apocalyptic number.

21111212100 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 21111212100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34249464144).

21111212100 is an abundant number, since it is smaller than the sum of its proper divisors (47387716188).

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

21111212100 is a wasteful number, since it uses less digits than its factorization.

21111212100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4775 (or 4731 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 12.

Adding to 21111212100 its reverse (121211112), we get a palindrome (21232423212).

The spelling of 21111212100 in words is "twenty-one billion, one hundred eleven million, two hundred twelve thousand, one hundred".