21711681 has 6 divisors (see below), whose sum is σ = 31361330. Its totient is φ = 14474448.

The previous prime is 21711619. The next prime is 21711709. The reversal of 21711681 is 18611712.

21711681 is nontrivially palindromic in base 16.

It can be written as a sum of positive squares in only one way, i.e., 20250000 + 1461681 = 4500^2 + 1209^2 .

It is not a de Polignac number, because 21711681 - 2¹⁷ = 21580609 is a prime.

It is a super-2 number, since 2×21711681² = 942794183691522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21711611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1206196 + ... + 1206213.

Almost surely, 2^21711681 is an apocalyptic number.

It is an amenable number.

21711681 is a deficient number, since it is larger than the sum of its proper divisors (9649649).

21711681 is a wasteful number, since it uses less digits than its factorization.

21711681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2412415 (or 2412412 counting only the distinct ones).

The product of its digits is 672, while the sum is 27.

The square root of 21711681 is about 4659.5794874645. The cubic root of 21711681 is about 278.9744841197.

The spelling of 21711681 in words is "twenty-one million, seven hundred eleven thousand, six hundred eighty-one".