21373561 has 6 divisors (see below), whose sum is σ = 23493386. Its totient is φ = 19430400.

The previous prime is 21373559. The next prime is 21373577. The reversal of 21373561 is 16537312.

It can be written as a sum of positive squares in only one way, i.e., 19360000 + 2013561 = 4400^2 + 1419^2 .

It is not a de Polignac number, because 21373561 - 2¹ = 21373559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21373501) 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 5 ways as a sum of consecutive naturals, for example, 88200 + ... + 88441.

Almost surely, 2^21373561 is an apocalyptic number.

It is an amenable number.

21373561 is a deficient number, since it is larger than the sum of its proper divisors (2119825).

21373561 is a wasteful number, since it uses less digits than its factorization.

21373561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176663 (or 176652 counting only the distinct ones).

The product of its digits is 3780, while the sum is 28.

The square root of 21373561 is about 4623.1548751908. The cubic root of 21373561 is about 277.5187271943.

The spelling of 21373561 in words is "twenty-one million, three hundred seventy-three thousand, five hundred sixty-one".