21691008 has 96 divisors (see below), whose sum is σ = 65769600. Its totient is φ = 6842880.

The previous prime is 21691003. The next prime is 21691013. The reversal of 21691008 is 80019612.

It is an interprime number because it is at equal distance from previous prime (21691003) and next prime (21691013).

It is a tau number, because it is divible by the number of its divisors (96).

It is not an unprimeable number, because it can be changed into a prime (21691003) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 21393 + ... + 22383.

It is an arithmetic number, because the mean of its divisors is an integer number (685100).

Almost surely, 2^21691008 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 21691008, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32884800).

21691008 is an abundant number, since it is smaller than the sum of its proper divisors (44078592).

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

21691008 is a wasteful number, since it uses less digits than its factorization.

21691008 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1030 (or 1015 counting only the distinct ones).

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

The square root of 21691008 is about 4657.3606259340. The cubic root of 21691008 is about 278.8859131960.

The spelling of 21691008 in words is "twenty-one million, six hundred ninety-one thousand, eight".