21081573 has 8 divisors (see below), whose sum is σ = 31232000. Its totient is φ = 14054364.

The previous prime is 21081569. The next prime is 21081589. The reversal of 21081573 is 37518012.

21081573 is a `hidden beast` number, since 2 + 10 + 81 + 573 = 666.

It is not a de Polignac number, because 21081573 - 2² = 21081569 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 780799 = 21081573 / (2 + 1 + 0 + 8 + 1 + 5 + 7 + 3).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081373) 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 7 ways as a sum of consecutive naturals, for example, 390373 + ... + 390426.

It is an arithmetic number, because the mean of its divisors is an integer number (3904000).

Almost surely, 2^21081573 is an apocalyptic number.

It is an amenable number.

21081573 is a deficient number, since it is larger than the sum of its proper divisors (10150427).

21081573 is an equidigital number, since it uses as much as digits as its factorization.

21081573 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 780808 (or 780802 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21081573 is about 4591.4674124946. The cubic root of 21081573 is about 276.2491842212.

Adding to 21081573 its reverse (37518012), we get a palindrome (58599585).

The spelling of 21081573 in words is "twenty-one million, eighty-one thousand, five hundred seventy-three".