21811680 has 336 divisors, whose sum is σ = 89241264. Its totient is φ = 4976640.

The previous prime is 21811679. The next prime is 21811717. The reversal of 21811680 is 8611812.

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 pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 1283032 + ... + 1283048.

It is an arithmetic number, because the mean of its divisors is an integer number (265599).

Almost surely, 2^21811680 is an apocalyptic number.

21811680 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 21811680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44620632).

21811680 is an abundant number, since it is smaller than the sum of its proper divisors (67429584).

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

21811680 is a wasteful number, since it uses less digits than its factorization.

21811680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61 (or 38 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 27.

The square root of 21811680 is about 4670.2976350550. The cubic root of 21811680 is about 279.4021256487.

The spelling of 21811680 in words is "twenty-one million, eight hundred eleven thousand, six hundred eighty".