21660534 has 48 divisors (see below), whose sum is σ = 55630848. Its totient is φ = 6187752.

The previous prime is 21660523. The next prime is 21660559. The reversal of 21660534 is 43506612.

21660534 is a `hidden beast` number, since 21 + 6 + 605 + 34 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 21660498 and 21660507.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 219 + ... + 6585.

It is an arithmetic number, because the mean of its divisors is an integer number (1158976).

Almost surely, 2^21660534 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21660534, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27815424).

21660534 is an abundant number, since it is smaller than the sum of its proper divisors (33970314).

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

21660534 is an equidigital number, since it uses as much as digits as its factorization.

21660534 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6391 (or 6379 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21660534 is about 4654.0878805626. The cubic root of 21660534 is about 278.7552484148.

The spelling of 21660534 in words is "twenty-one million, six hundred sixty thousand, five hundred thirty-four".