21711551 has 4 divisors (see below), whose sum is σ = 22035672. Its totient is φ = 21387432.

The previous prime is 21711541. The next prime is 21711577. The reversal of 21711551 is 15511712.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21711551 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 (21711541) 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, 161960 + ... + 162093.

It is an arithmetic number, because the mean of its divisors is an integer number (5508918).

Almost surely, 2^21711551 is an apocalyptic number.

21711551 is a deficient number, since it is larger than the sum of its proper divisors (324121).

21711551 is an equidigital number, since it uses as much as digits as its factorization.

21711551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 324120.

The product of its digits is 350, while the sum is 23.

The square root of 21711551 is about 4659.5655376870. The cubic root of 21711551 is about 278.9739273264.

The spelling of 21711551 in words is "twenty-one million, seven hundred eleven thousand, five hundred fifty-one".