21472921 has 4 divisors (see below), whose sum is σ = 22736052. Its totient is φ = 20209792.

The previous prime is 21472901. The next prime is 21472931. The reversal of 21472921 is 12927412.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18361225 + 3111696 = 4285^2 + 1764^2 .

It is a cyclic number.

It is not a de Polignac number, because 21472921 - 2¹⁹ = 20948633 is a prime.

It is a super-2 number, since 2×21472921² = 922172672544482, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21472921.

It is not an unprimeable number, because it can be changed into a prime (21472901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 631540 + ... + 631573.

It is an arithmetic number, because the mean of its divisors is an integer number (5684013).

Almost surely, 2^21472921 is an apocalyptic number.

It is an amenable number.

21472921 is a deficient number, since it is larger than the sum of its proper divisors (1263131).

21472921 is a wasteful number, since it uses less digits than its factorization.

21472921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1263130.

The product of its digits is 2016, while the sum is 28.

The square root of 21472921 is about 4633.8883240751. Note that the first 3 decimals coincide. The cubic root of 21472921 is about 277.9480994497.

The spelling of 21472921 in words is "twenty-one million, four hundred seventy-two thousand, nine hundred twenty-one".