21173709 has 4 divisors (see below), whose sum is σ = 28231616. Its totient is φ = 14115804.

The previous prime is 21173701. The next prime is 21173717. The reversal of 21173709 is 90737112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21173701) and next prime (21173717).

It is not a de Polignac number, because 21173709 - 2³ = 21173701 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21173701) 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, 3528949 + ... + 3528954.

It is an arithmetic number, because the mean of its divisors is an integer number (7057904).

Almost surely, 2^21173709 is an apocalyptic number.

It is an amenable number.

21173709 is a deficient number, since it is larger than the sum of its proper divisors (7057907).

21173709 is an equidigital number, since it uses as much as digits as its factorization.

21173709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7057906.

The product of its (nonzero) digits is 2646, while the sum is 30.

The square root of 21173709 is about 4601.4898674234. The cubic root of 21173709 is about 276.6510439397.

It can be divided in two parts, 211 and 73709, that added together give a triangular number (73920 = T₃₈₄).

The spelling of 21173709 in words is "twenty-one million, one hundred seventy-three thousand, seven hundred nine".