21113681 has 4 divisors (see below), whose sum is σ = 21471600. Its totient is φ = 20755764.

The previous prime is 21113671. The next prime is 21113689. The reversal of 21113681 is 18631112.

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 a de Polignac number, because none of the positive numbers 2^k-21113681 is a prime.

It is a super-2 number, since 2×21113681² = 891575050739522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21113689) 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, 178871 + ... + 178988.

It is an arithmetic number, because the mean of its divisors is an integer number (5367900).

Almost surely, 2^21113681 is an apocalyptic number.

It is an amenable number.

21113681 is a deficient number, since it is larger than the sum of its proper divisors (357919).

21113681 is an equidigital number, since it uses as much as digits as its factorization.

21113681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 357918.

The product of its digits is 288, while the sum is 23.

The square root of 21113681 is about 4594.9625678562. The cubic root of 21113681 is about 276.3893589226.

Adding to 21113681 its reverse (18631112), we get a palindrome (39744793).

The spelling of 21113681 in words is "twenty-one million, one hundred thirteen thousand, six hundred eighty-one".