21755691 has 12 divisors (see below), whose sum is σ = 31529368. Its totient is φ = 14455584.

The previous prime is 21755683. The next prime is 21755717. The reversal of 21755691 is 19655712.

21755691 is a `hidden beast` number, since 2 + 17 + 556 + 91 = 666.

It is not a de Polignac number, because 21755691 - 2³ = 21755683 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21755611) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1045 + ... + 6678.

Almost surely, 2^21755691 is an apocalyptic number.

21755691 is a deficient number, since it is larger than the sum of its proper divisors (9773677).

21755691 is a wasteful number, since it uses less digits than its factorization.

21755691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8042 (or 8039 counting only the distinct ones).

The product of its digits is 18900, while the sum is 36.

The square root of 21755691 is about 4664.2996258817. The cubic root of 21755691 is about 279.1628524713.

The spelling of 21755691 in words is "twenty-one million, seven hundred fifty-five thousand, six hundred ninety-one".