21640724 has 24 divisors (see below), whose sum is σ = 43380288. Its totient is φ = 9253440.

The previous prime is 21640721. The next prime is 21640747. The reversal of 21640724 is 42704612.

It is a junction number, because it is equal to n+sod(n) for n = 21640693 and 21640702.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640721) 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, 22232 + ... + 23184.

It is an arithmetic number, because the mean of its divisors is an integer number (1807512).

Almost surely, 2^21640724 is an apocalyptic number.

It is an amenable number.

21640724 is an abundant number, since it is smaller than the sum of its proper divisors (21739564).

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

21640724 is a wasteful number, since it uses less digits than its factorization.

21640724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1775 (or 1773 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 26.

The square root of 21640724 is about 4651.9591571724. The cubic root of 21640724 is about 278.6702424191.

The spelling of 21640724 in words is "twenty-one million, six hundred forty thousand, seven hundred twenty-four".