21691477 has 4 divisors (see below), whose sum is σ = 21711820. Its totient is φ = 21671136.

The previous prime is 21691459. The next prime is 21691489. The reversal of 21691477 is 77419612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12013156 + 9678321 = 3466^2 + 3111^2 .

It is a cyclic number.

It is not a de Polignac number, because 21691477 - 2⁷ = 21691349 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691447) 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, 8478 + ... + 10735.

It is an arithmetic number, because the mean of its divisors is an integer number (5427955).

Almost surely, 2^21691477 is an apocalyptic number.

It is an amenable number.

21691477 is a deficient number, since it is larger than the sum of its proper divisors (20343).

21691477 is a wasteful number, since it uses less digits than its factorization.

21691477 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20342.

The product of its digits is 21168, while the sum is 37.

The square root of 21691477 is about 4657.4109760681. The cubic root of 21691477 is about 278.8879231925.

The spelling of 21691477 in words is "twenty-one million, six hundred ninety-one thousand, four hundred seventy-seven".