21381673 has 4 divisors (see below), whose sum is σ = 21518020. Its totient is φ = 21245328.

The previous prime is 21381653. The next prime is 21381739. The reversal of 21381673 is 37618312.

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 9909904 + 11471769 = 3148^2 + 3387^2 .

It is a cyclic number.

It is not a de Polignac number, because 21381673 - 2⁹ = 21381161 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21381653) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 67938 + ... + 68251.

It is an arithmetic number, because the mean of its divisors is an integer number (5379505).

Almost surely, 2^21381673 is an apocalyptic number.

It is an amenable number.

21381673 is a deficient number, since it is larger than the sum of its proper divisors (136347).

21381673 is a wasteful number, since it uses less digits than its factorization.

21381673 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 136346.

The product of its digits is 6048, while the sum is 31.

The square root of 21381673 is about 4624.0321149404. The cubic root of 21381673 is about 277.5538320476.

Adding to 21381673 its reverse (37618312), we get a palindrome (58999985).

The spelling of 21381673 in words is "twenty-one million, three hundred eighty-one thousand, six hundred seventy-three".