21561451 has 8 divisors (see below), whose sum is σ = 21912800. Its totient is φ = 21212928.

The previous prime is 21561443. The next prime is 21561469. The reversal of 21561451 is 15416512.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21561451 - 2³ = 21561443 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21561401) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18745 + ... + 19861.

It is an arithmetic number, because the mean of its divisors is an integer number (2739100).

Almost surely, 2^21561451 is an apocalyptic number.

21561451 is a deficient number, since it is larger than the sum of its proper divisors (351349).

21561451 is a wasteful number, since it uses less digits than its factorization.

21561451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1413.

The product of its digits is 1200, while the sum is 25.

The square root of 21561451 is about 4643.4309513548. The cubic root of 21561451 is about 278.3295567234.

Adding to 21561451 its reverse (15416512), we get a palindrome (36977963).

The spelling of 21561451 in words is "twenty-one million, five hundred sixty-one thousand, four hundred fifty-one".