21531708 has 54 divisors (see below), whose sum is σ = 59837232. Its totient is φ = 6523440.

The previous prime is 21531689. The next prime is 21531709. The reversal of 21531708 is 80713512.

It is a super-2 number, since 2×21531708² = 927228898794528, which contains 22 as substring.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531709) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1885 + ... + 6827.

Almost surely, 2^21531708 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 21531708, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29918616).

21531708 is an abundant number, since it is smaller than the sum of its proper divisors (38305524).

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

21531708 is a wasteful number, since it uses less digits than its factorization.

21531708 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4975 (or 4959 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21531708 is about 4640.2271496124. The cubic root of 21531708 is about 278.2015170187.

The spelling of 21531708 in words is "twenty-one million, five hundred thirty-one thousand, seven hundred eight".