21605716 has 12 divisors (see below), whose sum is σ = 41247360. Its totient is φ = 9820760.

The previous prime is 21605711. The next prime is 21605747. The reversal of 21605716 is 61750612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605711) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 245476 + ... + 245563.

It is an arithmetic number, because the mean of its divisors is an integer number (3437280).

Almost surely, 2^21605716 is an apocalyptic number.

It is an amenable number.

21605716 is a deficient number, since it is larger than the sum of its proper divisors (19641644).

21605716 is a wasteful number, since it uses less digits than its factorization.

21605716 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 491054 (or 491052 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21605716 is about 4648.1949184603. The cubic root of 21605716 is about 278.5198938888.

Subtracting 21605716 from its reverse (61750612), we obtain a square (40144896 = 6336²).

The spelling of 21605716 in words is "twenty-one million, six hundred five thousand, seven hundred sixteen".