21531471 has 8 divisors (see below), whose sum is σ = 30917040. Its totient is φ = 13250112.

The previous prime is 21531443. The next prime is 21531479. The reversal of 21531471 is 17413512.

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

It is not a de Polignac number, because 21531471 - 2⁵ = 21531439 is a prime.

It is a super-3 number, since 3×21531471³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531479) 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, 276006 + ... + 276083.

It is an arithmetic number, because the mean of its divisors is an integer number (3864630).

Almost surely, 2^21531471 is an apocalyptic number.

21531471 is a deficient number, since it is larger than the sum of its proper divisors (9385569).

21531471 is a wasteful number, since it uses less digits than its factorization.

21531471 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 552105.

The product of its digits is 840, while the sum is 24.

The square root of 21531471 is about 4640.2016119992. The cubic root of 21531471 is about 278.2004962915.

Adding to 21531471 its reverse (17413512), we get a palindrome (38944983).

The spelling of 21531471 in words is "twenty-one million, five hundred thirty-one thousand, four hundred seventy-one".