21701681 has 4 divisors (see below), whose sum is σ = 21711600. Its totient is φ = 21691764.

The previous prime is 21701651. The next prime is 21701683. The reversal of 21701681 is 18610712.

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 21701681 - 2²² = 17507377 is a prime.

It is a super-2 number, since 2×21701681² = 941925916451522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21701681.

It is not an unprimeable number, because it can be changed into a prime (21701683) 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, 71 + ... + 6588.

It is an arithmetic number, because the mean of its divisors is an integer number (5427900).

Almost surely, 2^21701681 is an apocalyptic number.

It is an amenable number.

21701681 is a deficient number, since it is larger than the sum of its proper divisors (9919).

21701681 is an equidigital number, since it uses as much as digits as its factorization.

21701681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9918.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 21701681 is about 4658.5063056735. The cubic root of 21701681 is about 278.9316473743.

The spelling of 21701681 in words is "twenty-one million, seven hundred one thousand, six hundred eighty-one".