21426721 has 4 divisors (see below), whose sum is σ = 21616452. Its totient is φ = 21236992.

The previous prime is 21426719. The next prime is 21426733. The reversal of 21426721 is 12762412.

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 1535121 + 19891600 = 1239^2 + 4460^2 .

It is a cyclic number.

It is not a de Polignac number, because 21426721 - 2¹ = 21426719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21426701) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 94696 + ... + 94921.

It is an arithmetic number, because the mean of its divisors is an integer number (5404113).

Almost surely, 2^21426721 is an apocalyptic number.

It is an amenable number.

21426721 is a deficient number, since it is larger than the sum of its proper divisors (189731).

21426721 is a wasteful number, since it uses less digits than its factorization.

21426721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 189730.

The product of its digits is 1344, while the sum is 25.

The square root of 21426721 is about 4628.9006254185. The cubic root of 21426721 is about 277.7486168440.

The spelling of 21426721 in words is "twenty-one million, four hundred twenty-six thousand, seven hundred twenty-one".