21404451 has 4 divisors (see below), whose sum is σ = 28539272. Its totient is φ = 14269632.

The previous prime is 21404437. The next prime is 21404459. The reversal of 21404451 is 15440412.

It is a happy number.

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

It is not a de Polignac number, because 21404451 - 2¹⁵ = 21371683 is a prime.

It is a super-2 number, since 2×21404451² = 916301045222802, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21404459) 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, 3567406 + ... + 3567411.

It is an arithmetic number, because the mean of its divisors is an integer number (7134818).

Almost surely, 2^21404451 is an apocalyptic number.

21404451 is a deficient number, since it is larger than the sum of its proper divisors (7134821).

21404451 is an equidigital number, since it uses as much as digits as its factorization.

21404451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7134820.

The product of its (nonzero) digits is 640, while the sum is 21.

The square root of 21404451 is about 4626.4944612525. The cubic root of 21404451 is about 277.6523568843.

Adding to 21404451 its reverse (15440412), we get a palindrome (36844863).

The spelling of 21404451 in words is "twenty-one million, four hundred four thousand, four hundred fifty-one".