21709821 has 8 divisors (see below), whose sum is σ = 33081664. Its totient is φ = 12405600.

The previous prime is 21709819. The next prime is 21709823. The reversal of 21709821 is 12890712.

It is an interprime number because it is at equal distance from previous prime (21709819) and next prime (21709823).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21709821 - 2¹ = 21709819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21709823) 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, 516880 + ... + 516921.

It is an arithmetic number, because the mean of its divisors is an integer number (4135208).

Almost surely, 2^21709821 is an apocalyptic number.

21709821 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21709821 is a deficient number, since it is larger than the sum of its proper divisors (11371843).

21709821 is a wasteful number, since it uses less digits than its factorization.

21709821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1033811.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21709821 is about 4659.3798943636. The cubic root of 21709821 is about 278.9665174809.

The spelling of 21709821 in words is "twenty-one million, seven hundred nine thousand, eight hundred twenty-one".