21605161 has 4 divisors (see below), whose sum is σ = 21737872. Its totient is φ = 21472452.

The previous prime is 21605159. The next prime is 21605167. The reversal of 21605161 is 16150612.

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 21605161 - 2¹ = 21605159 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21605167) 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, 66111 + ... + 66436.

It is an arithmetic number, because the mean of its divisors is an integer number (5434468).

Almost surely, 2^21605161 is an apocalyptic number.

It is an amenable number.

21605161 is a deficient number, since it is larger than the sum of its proper divisors (132711).

21605161 is a wasteful number, since it uses less digits than its factorization.

21605161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132710.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21605161 is about 4648.1352174824. The cubic root of 21605161 is about 278.5175090282.

Adding to 21605161 its reverse (16150612), we get a palindrome (37755773).

The spelling of 21605161 in words is "twenty-one million, six hundred five thousand, one hundred sixty-one".