21565640 has 16 divisors (see below), whose sum is σ = 48522780. Its totient is φ = 8626240.

The previous prime is 21565633. The next prime is 21565667. The reversal of 21565640 is 4656512.

It can be written as a sum of positive squares in 2 ways, for example, as 20593444 + 972196 = 4538^2 + 986^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 269531 + ... + 269610.

Almost surely, 2^21565640 is an apocalyptic number.

21565640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21565640 is an abundant number, since it is smaller than the sum of its proper divisors (26957140).

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

21565640 is a wasteful number, since it uses less digits than its factorization.

21565640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 539152 (or 539148 counting only the distinct ones).

The product of its (nonzero) digits is 7200, while the sum is 29.

The square root of 21565640 is about 4643.8819967781. The cubic root of 21565640 is about 278.3475803561.

The spelling of 21565640 in words is "twenty-one million, five hundred sixty-five thousand, six hundred forty".