21642661 has 4 divisors (see below), whose sum is σ = 21657312. Its totient is φ = 21628012.

The previous prime is 21642637. The next prime is 21642667. The reversal of 21642661 is 16624612.

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 21642661 - 2¹¹ = 21640613 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 (21642667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4825 + ... + 8158.

It is an arithmetic number, because the mean of its divisors is an integer number (5414328).

Almost surely, 2^21642661 is an apocalyptic number.

It is an amenable number.

21642661 is a deficient number, since it is larger than the sum of its proper divisors (14651).

21642661 is a wasteful number, since it uses less digits than its factorization.

21642661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14650.

The product of its digits is 3456, while the sum is 28.

The square root of 21642661 is about 4652.1673443676. The cubic root of 21642661 is about 278.6785564994.

The spelling of 21642661 in words is "twenty-one million, six hundred forty-two thousand, six hundred sixty-one".