21709540 has 24 divisors (see below), whose sum is σ = 45739512. Its totient is φ = 8655360.

The previous prime is 21709531. The next prime is 21709553. The reversal of 21709540 is 4590712.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 2490084 + 19219456 = 1578^2 + 4384^2 .

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 21709499 and 21709508.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5130 + ... + 8350.

It is an arithmetic number, because the mean of its divisors is an integer number (1905813).

Almost surely, 2^21709540 is an apocalyptic number.

21709540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21709540 is an abundant number, since it is smaller than the sum of its proper divisors (24029972).

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

21709540 is a wasteful number, since it uses less digits than its factorization.

21709540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3567 (or 3565 counting only the distinct ones).

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

The square root of 21709540 is about 4659.3497400388. The cubic root of 21709540 is about 278.9653138793.

The spelling of 21709540 in words is "twenty-one million, seven hundred nine thousand, five hundred forty".