21691841 has 4 divisors (see below), whose sum is σ = 21707952. Its totient is φ = 21675732.

The previous prime is 21691793. The next prime is 21691843. The reversal of 21691841 is 14819612.

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.

It is a cyclic number.

It is not a de Polignac number, because 21691841 - 2⁶ = 21691777 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21691798 and 21691807.

It is not an unprimeable number, because it can be changed into a prime (21691843) 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, 5831 + ... + 8796.

It is an arithmetic number, because the mean of its divisors is an integer number (5426988).

Almost surely, 2^21691841 is an apocalyptic number.

It is an amenable number.

21691841 is a deficient number, since it is larger than the sum of its proper divisors (16111).

21691841 is a wasteful number, since it uses less digits than its factorization.

21691841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16110.

The product of its digits is 3456, while the sum is 32.

The square root of 21691841 is about 4657.4500534091. The cubic root of 21691841 is about 278.8894831698.

The spelling of 21691841 in words is "twenty-one million, six hundred ninety-one thousand, eight hundred forty-one".