21451557 has 4 divisors (see below), whose sum is σ = 28602080. Its totient is φ = 14301036.

The previous prime is 21451537. The next prime is 21451559. The reversal of 21451557 is 75515412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21451557 - 2²⁰ = 20402981 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 (21451559) 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, 3575257 + ... + 3575262.

It is an arithmetic number, because the mean of its divisors is an integer number (7150520).

Almost surely, 2^21451557 is an apocalyptic number.

It is an amenable number.

21451557 is a deficient number, since it is larger than the sum of its proper divisors (7150523).

21451557 is an equidigital number, since it uses as much as digits as its factorization.

21451557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7150522.

The product of its digits is 7000, while the sum is 30.

The square root of 21451557 is about 4631.5825589101. The cubic root of 21451557 is about 277.8558894580.

Adding to 21451557 its reverse (75515412), we get a palindrome (96966969).

The spelling of 21451557 in words is "twenty-one million, four hundred fifty-one thousand, five hundred fifty-seven".