21258161 has 4 divisors (see below), whose sum is σ = 21453300. Its totient is φ = 21063024.

The previous prime is 21258151. The next prime is 21258173. The reversal of 21258161 is 16185212.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9486400 + 11771761 = 3080^2 + 3431^2 .

It is a cyclic number.

It is not a de Polignac number, because 21258161 - 2¹⁴ = 21241777 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21258161.

It is not an unprimeable number, because it can be changed into a prime (21258101) 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, 97406 + ... + 97623.

It is an arithmetic number, because the mean of its divisors is an integer number (5363325).

Almost surely, 2^21258161 is an apocalyptic number.

21258161 is the 2465-th centered heptagonal number.

It is an amenable number.

21258161 is a deficient number, since it is larger than the sum of its proper divisors (195139).

21258161 is a wasteful number, since it uses less digits than its factorization.

21258161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 195138.

The product of its digits is 960, while the sum is 26.

The square root of 21258161 is about 4610.6573284077. The cubic root of 21258161 is about 277.0183664572.

The spelling of 21258161 in words is "twenty-one million, two hundred fifty-eight thousand, one hundred sixty-one".