21591451 has 4 divisors (see below), whose sum is σ = 24675952. Its totient is φ = 18506952.

The previous prime is 21591443. The next prime is 21591481. The reversal of 21591451 is 15419512.

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

It is a cyclic number.

It is not a de Polignac number, because 21591451 - 2³ = 21591443 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21591421) 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, 1542240 + ... + 1542253.

It is an arithmetic number, because the mean of its divisors is an integer number (6168988).

Almost surely, 2^21591451 is an apocalyptic number.

21591451 is a deficient number, since it is larger than the sum of its proper divisors (3084501).

21591451 is an equidigital number, since it uses as much as digits as its factorization.

21591451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3084500.

The product of its digits is 1800, while the sum is 28.

The square root of 21591451 is about 4646.6601984651. The cubic root of 21591451 is about 278.4585835546.

The spelling of 21591451 in words is "twenty-one million, five hundred ninety-one thousand, four hundred fifty-one".