21161257 has 8 divisors (see below), whose sum is σ = 23219784. Its totient is φ = 19164288.

The previous prime is 21161237. The next prime is 21161279. The reversal of 21161257 is 75216112.

It can be written as a sum of positive squares in 4 ways, for example, as 5669161 + 15492096 = 2381^2 + 3936^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21161257 - 2²³ = 12772649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21161227) 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 7 ways as a sum of consecutive naturals, for example, 14668 + ... + 16045.

It is an arithmetic number, because the mean of its divisors is an integer number (2902473).

Almost surely, 2^21161257 is an apocalyptic number.

It is an amenable number.

21161257 is a deficient number, since it is larger than the sum of its proper divisors (2058527).

21161257 is a wasteful number, since it uses less digits than its factorization.

21161257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30779.

The product of its digits is 840, while the sum is 25.

The square root of 21161257 is about 4600.1366284057. The cubic root of 21161257 is about 276.5968016037.

Adding to 21161257 its reverse (75216112), we get a palindrome (96377369).

The spelling of 21161257 in words is "twenty-one million, one hundred sixty-one thousand, two hundred fifty-seven".