21111681 has 16 divisors (see below), whose sum is σ = 29275200. Its totient is φ = 13516608.

The previous prime is 21111617. The next prime is 21111683. The reversal of 21111681 is 18611112.

It is a happy number.

It is not a de Polignac number, because 21111681 - 2⁶ = 21111617 is a prime.

It is a super-2 number, since 2×21111681² = 891406149291522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21111683) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19215 + ... + 20283.

It is an arithmetic number, because the mean of its divisors is an integer number (1829700).

Almost surely, 2^21111681 is an apocalyptic number.

It is an amenable number.

21111681 is a deficient number, since it is larger than the sum of its proper divisors (8163519).

21111681 is a wasteful number, since it uses less digits than its factorization.

21111681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1328.

The product of its digits is 96, while the sum is 21.

The square root of 21111681 is about 4594.7449330730. The cubic root of 21111681 is about 276.3806316244.

Adding to 21111681 its reverse (18611112), we get a palindrome (39722793).

The spelling of 21111681 in words is "twenty-one million, one hundred eleven thousand, six hundred eighty-one".