21162561 has 24 divisors (see below), whose sum is σ = 34555680. Its totient is φ = 11454912.

The previous prime is 21162551. The next prime is 21162613. The reversal of 21162561 is 16526112.

It is not a de Polignac number, because 21162561 - 2¹⁰ = 21161537 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21162521) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 996 + ... + 6581.

It is an arithmetic number, because the mean of its divisors is an integer number (1439820).

Almost surely, 2^21162561 is an apocalyptic number.

21162561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21162561 is a deficient number, since it is larger than the sum of its proper divisors (13393119).

21162561 is a wasteful number, since it uses less digits than its factorization.

21162561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7613 (or 7606 counting only the distinct ones).

The product of its digits is 720, while the sum is 24.

The square root of 21162561 is about 4600.2783611429. The cubic root of 21162561 is about 276.6024829742.

Adding to 21162561 its reverse (16526112), we get a palindrome (37688673).

The spelling of 21162561 in words is "twenty-one million, one hundred sixty-two thousand, five hundred sixty-one".