21181891600 has 135 divisors (see below), whose sum is σ = 53849455293. Its totient is φ = 8005864320.

The previous prime is 21181891583. The next prime is 21181891651. The reversal of 21181891600 is 619818112.

The square root of 21181891600 is 145540.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 7625480976 + 13556410624 = 87324^2 + 116432^2 .

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21181891600.

It is an unprimeable number.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 55305009 + ... + 55305391.

Almost surely, 2^21181891600 is an apocalyptic number.

21181891600 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21181891600 is the 145540-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21181891600

21181891600 is an abundant number, since it is smaller than the sum of its proper divisors (32667563693).

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

21181891600 is an equidigital number, since it uses as much as digits as its factorization.

21181891600 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 822 (or 409 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 37.

The spelling of 21181891600 in words is "twenty-one billion, one hundred eighty-one million, eight hundred ninety-one thousand, six hundred".