21091968 has 128 divisors (see below), whose sum is σ = 66096000. Its totient is φ = 6598656.

The previous prime is 21091949. The next prime is 21091979. The reversal of 21091968 is 86919012.

It is a tau number, because it is divible by the number of its divisors (128).

It is a super-2 number, since 2×21091968² = 889742228226048, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 58573 + ... + 58931.

It is an arithmetic number, because the mean of its divisors is an integer number (516375).

Almost surely, 2^21091968 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21091968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33048000).

21091968 is an abundant number, since it is smaller than the sum of its proper divisors (45004032).

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

21091968 is a wasteful number, since it uses less digits than its factorization.

21091968 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 399 (or 381 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 21091968 is about 4592.5992640334. The cubic root of 21091968 is about 276.2945815044.

The spelling of 21091968 in words is "twenty-one million, ninety-one thousand, nine hundred sixty-eight".