21712821 has 32 divisors (see below), whose sum is σ = 32890368. Its totient is φ = 12648960.

The previous prime is 21712819. The next prime is 21712843. The reversal of 21712821 is 12821712.

It is not a de Polignac number, because 21712821 - 2¹ = 21712819 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21712791 and 21712800.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21712861) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 58980 + ... + 59346.

It is an arithmetic number, because the mean of its divisors is an integer number (1027824).

Almost surely, 2^21712821 is an apocalyptic number.

It is an amenable number.

21712821 is a deficient number, since it is larger than the sum of its proper divisors (11177547).

21712821 is a wasteful number, since it uses less digits than its factorization.

21712821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 461.

The product of its digits is 448, while the sum is 24.

The square root of 21712821 is about 4659.7018144941. The cubic root of 21712821 is about 278.9793666734.

The spelling of 21712821 in words is "twenty-one million, seven hundred twelve thousand, eight hundred twenty-one".