21631523 has 4 divisors (see below), whose sum is σ = 22572048. Its totient is φ = 20691000.

The previous prime is 21631517. The next prime is 21631541. The reversal of 21631523 is 32513612.

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

It is a cyclic number.

It is not a de Polignac number, because 21631523 - 2⁴ = 21631507 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 940501 = 21631523 / (2 + 1 + 6 + 3 + 1 + 5 + 2 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21631513) 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, 470228 + ... + 470273.

It is an arithmetic number, because the mean of its divisors is an integer number (5643012).

Almost surely, 2^21631523 is an apocalyptic number.

21631523 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21631523 is a deficient number, since it is larger than the sum of its proper divisors (940525).

21631523 is an equidigital number, since it uses as much as digits as its factorization.

21631523 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 940524.

The product of its digits is 1080, while the sum is 23.

The square root of 21631523 is about 4650.9701138580. The cubic root of 21631523 is about 278.6307426874.

The spelling of 21631523 in words is "twenty-one million, six hundred thirty-one thousand, five hundred twenty-three".