21661008 has 40 divisors (see below), whose sum is σ = 56642208. Its totient is φ = 7132032.

The previous prime is 21661001. The next prime is 21661027. The reversal of 21661008 is 80016612.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661001) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1266 + ... + 6702.

Almost surely, 2^21661008 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 21661008, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28321104).

21661008 is an abundant number, since it is smaller than the sum of its proper divisors (34981200).

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

21661008 is a wasteful number, since it uses less digits than its factorization.

21661008 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5531 (or 5525 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 24.

The square root of 21661008 is about 4654.1388032589. The cubic root of 21661008 is about 278.7572817445.

The spelling of 21661008 in words is "twenty-one million, six hundred sixty-one thousand, eight".