21967681 has 4 divisors (see below), whose sum is σ = 22099392. Its totient is φ = 21835972.

The previous prime is 21967669. The next prime is 21967709. The reversal of 21967681 is 18676912.

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 21967681 - 2¹³ = 21959489 is a prime.

It is a super-2 number, since 2×21967681² = 965158017035522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21967651) 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, 65605 + ... + 65938.

It is an arithmetic number, because the mean of its divisors is an integer number (5524848).

Almost surely, 2^21967681 is an apocalyptic number.

It is an amenable number.

21967681 is a deficient number, since it is larger than the sum of its proper divisors (131711).

21967681 is a wasteful number, since it uses less digits than its factorization.

21967681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131710.

The product of its digits is 36288, while the sum is 40.

The square root of 21967681 is about 4686.9692766222. The cubic root of 21967681 is about 280.0666550496.

The spelling of 21967681 in words is "twenty-one million, nine hundred sixty-seven thousand, six hundred eighty-one".