21631361 has 18 divisors (see below), whose sum is σ = 24065730. Its totient is φ = 19436032.

The previous prime is 21631349. The next prime is 21631387. The reversal of 21631361 is 16313612.

It is a happy number.

It can be written as a sum of positive squares in 9 ways, for example, as 1210000 + 20421361 = 1100^2 + 4519^2 .

It is not a de Polignac number, because 21631361 - 2⁶ = 21631297 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21631301) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 243005 + ... + 243093.

It is an arithmetic number, because the mean of its divisors is an integer number (1336985).

Almost surely, 2^21631361 is an apocalyptic number.

It is an amenable number.

21631361 is a deficient number, since it is larger than the sum of its proper divisors (2434369).

21631361 is an equidigital number, since it uses as much as digits as its factorization.

21631361 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 181 (or 135 counting only the distinct ones).

The product of its digits is 648, while the sum is 23.

The square root of 21631361 is about 4650.9526981039. The cubic root of 21631361 is about 278.6300471239.

Adding to 21631361 its reverse (16313612), we get a palindrome (37944973).

The spelling of 21631361 in words is "twenty-one million, six hundred thirty-one thousand, three hundred sixty-one".