21554591 has 4 divisors (see below), whose sum is σ = 21709800. Its totient is φ = 21399384.

The previous prime is 21554581. The next prime is 21554593. The reversal of 21554591 is 19545512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21554591 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21554593) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 77396 + ... + 77673.

It is an arithmetic number, because the mean of its divisors is an integer number (5427450).

Almost surely, 2^21554591 is an apocalyptic number.

21554591 is a deficient number, since it is larger than the sum of its proper divisors (155209).

21554591 is a wasteful number, since it uses less digits than its factorization.

21554591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 155208.

The product of its digits is 9000, while the sum is 32.

The square root of 21554591 is about 4642.6922146530. The cubic root of 21554591 is about 278.3000357775.

The spelling of 21554591 in words is "twenty-one million, five hundred fifty-four thousand, five hundred ninety-one".