21661131 has 4 divisors (see below), whose sum is σ = 28881512. Its totient is φ = 14440752.

The previous prime is 21661109. The next prime is 21661141. The reversal of 21661131 is 13116612.

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

It is not a de Polignac number, because 21661131 - 2⁹ = 21660619 is a prime.

It is a super-2 number, since 2×21661131² = 938409192398322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21661098 and 21661107.

It is not an unprimeable number, because it can be changed into a prime (21661141) 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, 3610186 + ... + 3610191.

It is an arithmetic number, because the mean of its divisors is an integer number (7220378).

Almost surely, 2^21661131 is an apocalyptic number.

21661131 is a deficient number, since it is larger than the sum of its proper divisors (7220381).

21661131 is an equidigital number, since it uses as much as digits as its factorization.

21661131 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7220380.

The product of its digits is 216, while the sum is 21.

The square root of 21661131 is about 4654.1520172852. The cubic root of 21661131 is about 278.7578093759.

Adding to 21661131 its reverse (13116612), we get a palindrome (34777743).

The spelling of 21661131 in words is "twenty-one million, six hundred sixty-one thousand, one hundred thirty-one".