21991400 has 48 divisors (see below), whose sum is σ = 52794240. Its totient is φ = 8510400.

The previous prime is 21991397. The next prime is 21991433. The reversal of 21991400 is 419912.

21991400 = T₂₉₁ + T₂₉₂ + ... + T₅₃₈.

It is a self number, because there is not a number n which added to its sum of digits gives 21991400.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4427 + ... + 7973.

It is an arithmetic number, because the mean of its divisors is an integer number (1099880).

Almost surely, 2^21991400 is an apocalyptic number.

21991400 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 21991400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26397120).

21991400 is an abundant number, since it is smaller than the sum of its proper divisors (30802840).

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

21991400 is a wasteful number, since it uses less digits than its factorization.

21991400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3594 (or 3585 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 21991400 is about 4689.4989071328. The cubic root of 21991400 is about 280.1674168854.

It can be divided in two parts, 219 and 91400, that added together give a palindrome (91619).

The spelling of 21991400 in words is "twenty-one million, nine hundred ninety-one thousand, four hundred".