21391191800 has 192 divisors, whose sum is σ = 60472915200. Its totient is φ = 6935500800.

The previous prime is 21391191799. The next prime is 21391191869. The reversal of 21391191800 is 819119312.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 695549 + ... + 725651.

It is an arithmetic number, because the mean of its divisors is an integer number (314963100).

Almost surely, 2^21391191800 is an apocalyptic number.

21391191800 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 21391191800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30236457600).

21391191800 is an abundant number, since it is smaller than the sum of its proper divisors (39081723400).

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

21391191800 is a wasteful number, since it uses less digits than its factorization.

21391191800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30166 (or 30157 counting only the distinct ones).

The product of its (nonzero) digits is 3888, while the sum is 35.

The spelling of 21391191800 in words is "twenty-one billion, three hundred ninety-one million, one hundred ninety-one thousand, eight hundred".