21657040 has 40 divisors (see below), whose sum is σ = 50630688. Its totient is φ = 8615040.

The previous prime is 21657029. The next prime is 21657043. The reversal of 21657040 is 4075612.

It is a tau number, because it is divible by the number of its divisors (40).

It is a hoax number, since the sum of its digits (25) coincides with the sum of the digits of its distinct prime factors.

It is a plaindrome in base 9.

It is a zygodrome in base 9.

It is a junction number, because it is equal to n+sod(n) for n = 21656996 and 21657014.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21657043) 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, 16239 + ... + 17521.

Almost surely, 2^21657040 is an apocalyptic number.

21657040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21657040 is an abundant number, since it is smaller than the sum of its proper divisors (28973648).

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

21657040 is a wasteful number, since it uses less digits than its factorization.

21657040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1507 (or 1501 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 25.

The square root of 21657040 is about 4653.7124964914. The cubic root of 21657040 is about 278.7402591997.

The spelling of 21657040 in words is "twenty-one million, six hundred fifty-seven thousand, forty".