21547661 has 4 divisors (see below), whose sum is σ = 21570912. Its totient is φ = 21524412.

The previous prime is 21547657. The next prime is 21547679. The reversal of 21547661 is 16674512.

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 21547661 - 2² = 21547657 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 (21547621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10175 + ... + 12108.

It is an arithmetic number, because the mean of its divisors is an integer number (5392728).

Almost surely, 2^21547661 is an apocalyptic number.

It is an amenable number.

21547661 is a deficient number, since it is larger than the sum of its proper divisors (23251).

21547661 is an equidigital number, since it uses as much as digits as its factorization.

21547661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23250.

The product of its digits is 10080, while the sum is 32.

The square root of 21547661 is about 4641.9458204507. The cubic root of 21547661 is about 278.2702072370.

The spelling of 21547661 in words is "twenty-one million, five hundred forty-seven thousand, six hundred sixty-one".