21205151 has 4 divisors (see below), whose sum is σ = 23132904. Its totient is φ = 19277400.

The previous prime is 21205139. The next prime is 21205157. The reversal of 21205151 is 15150212.

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 21205151 - 2¹⁸ = 20943007 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 (21205157) 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, 963860 + ... + 963881.

It is an arithmetic number, because the mean of its divisors is an integer number (5783226).

Almost surely, 2^21205151 is an apocalyptic number.

21205151 is a deficient number, since it is larger than the sum of its proper divisors (1927753).

21205151 is a wasteful number, since it uses less digits than its factorization.

21205151 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1927752.

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21205151 is about 4604.9051021709. The cubic root of 21205151 is about 276.7879143083.

Adding to 21205151 its reverse (15150212), we get a palindrome (36355363).

The spelling of 21205151 in words is "twenty-one million, two hundred five thousand, one hundred fifty-one".