21181373 has 4 divisors (see below), whose sum is σ = 21191520. Its totient is φ = 21171228.

The previous prime is 21181343. The next prime is 21181387. The reversal of 21181373 is 37318112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21181373 - 2⁶ = 21181309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21181343) 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, 665 + ... + 6542.

It is an arithmetic number, because the mean of its divisors is an integer number (5297880).

Almost surely, 2^21181373 is an apocalyptic number.

It is an amenable number.

21181373 is a deficient number, since it is larger than the sum of its proper divisors (10147).

21181373 is an equidigital number, since it uses as much as digits as its factorization.

21181373 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10146.

The product of its digits is 1008, while the sum is 26.

The square root of 21181373 is about 4602.3225658356. The cubic root of 21181373 is about 276.6844186284.

Adding to 21181373 its reverse (37318112), we get a palindrome (58499485).

The spelling of 21181373 in words is "twenty-one million, one hundred eighty-one thousand, three hundred seventy-three".