21664151 has 4 divisors (see below), whose sum is σ = 22031400. Its totient is φ = 21296904.

The previous prime is 21664147. The next prime is 21664163. The reversal of 21664151 is 15146612.

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

It is a cyclic number.

It is not a de Polignac number, because 21664151 - 2² = 21664147 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21664151.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664141) 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, 183536 + ... + 183653.

It is an arithmetic number, because the mean of its divisors is an integer number (5507850).

Almost surely, 2^21664151 is an apocalyptic number.

21664151 is a deficient number, since it is larger than the sum of its proper divisors (367249).

21664151 is an equidigital number, since it uses as much as digits as its factorization.

21664151 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 367248.

The product of its digits is 1440, while the sum is 26.

The square root of 21664151 is about 4654.4764474643. The cubic root of 21664151 is about 278.7707636004.

The spelling of 21664151 in words is "twenty-one million, six hundred sixty-four thousand, one hundred fifty-one".