21161521 has 4 divisors (see below), whose sum is σ = 21733492. Its totient is φ = 20589552.

The previous prime is 21161519. The next prime is 21161527. The reversal of 21161521 is 12516112.

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 19044496 + 2117025 = 4364^2 + 1455^2 .

It is a cyclic number.

It is not a de Polignac number, because 21161521 - 2¹ = 21161519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21161527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 285930 + ... + 286003.

It is an arithmetic number, because the mean of its divisors is an integer number (5433373).

Almost surely, 2^21161521 is an apocalyptic number.

It is an amenable number.

21161521 is a deficient number, since it is larger than the sum of its proper divisors (571971).

21161521 is an equidigital number, since it uses as much as digits as its factorization.

21161521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 571970.

The product of its digits is 120, while the sum is 19.

The square root of 21161521 is about 4600.1653231161. The cubic root of 21161521 is about 276.5979518387.

Adding to 21161521 its reverse (12516112), we get a palindrome (33677633).

It can be divided in two parts, 2116 and 1521, that multiplied together give a square (3218436 = 1794²).

The spelling of 21161521 in words is "twenty-one million, one hundred sixty-one thousand, five hundred twenty-one".