21691800 has 240 divisors, whose sum is σ = 81921840. Its totient is φ = 5287680.

The previous prime is 21691793. The next prime is 21691843. The reversal of 21691800 is 819612.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 210549 + ... + 210651.

It is an arithmetic number, because the mean of its divisors is an integer number (341341).

Almost surely, 2^21691800 is an apocalyptic number.

21691800 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 21691800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40960920).

21691800 is an abundant number, since it is smaller than the sum of its proper divisors (60230040).

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

21691800 is a wasteful number, since it uses less digits than its factorization.

21691800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144 (or 126 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 21691800 is about 4657.4456518568. The cubic root of 21691800 is about 278.8893074589.

It can be divided in two parts, 2169 and 1800, that added together give a square (3969 = 63²).

The spelling of 21691800 in words is "twenty-one million, six hundred ninety-one thousand, eight hundred".