21331551 has 8 divisors (see below), whose sum is σ = 28488240. Its totient is φ = 14197952.

The previous prime is 21331543. The next prime is 21331567. The reversal of 21331551 is 15513312.

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 21331551 - 2³ = 21331543 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331451) 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, 3486 + ... + 7403.

It is an arithmetic number, because the mean of its divisors is an integer number (3561030).

Almost surely, 2^21331551 is an apocalyptic number.

21331551 is a deficient number, since it is larger than the sum of its proper divisors (7156689).

21331551 is a wasteful number, since it uses less digits than its factorization.

21331551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11545.

The product of its digits is 450, while the sum is 21.

The square root of 21331551 is about 4618.6092062438. The cubic root of 21331551 is about 277.3367857694.

Adding to 21331551 its reverse (15513312), we get a palindrome (36844863).

The spelling of 21331551 in words is "twenty-one million, three hundred thirty-one thousand, five hundred fifty-one".