21172709 has 2 divisors, whose sum is σ = 21172710. Its totient is φ = 21172708.

The previous prime is 21172693. The next prime is 21172717. The reversal of 21172709 is 90727112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18515809 + 2656900 = 4303^2 + 1630^2 .

It is a cyclic number.

It is not a de Polignac number, because 21172709 - 2⁴ = 21172693 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21172009) 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 as a sum of consecutive naturals, namely, 10586354 + 10586355.

It is an arithmetic number, because the mean of its divisors is an integer number (10586355).

Almost surely, 2^21172709 is an apocalyptic number.

It is an amenable number.

21172709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21172709 is an equidigital number, since it uses as much as digits as its factorization.

21172709 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1764, while the sum is 29.

The square root of 21172709 is about 4601.3812056816. The cubic root of 21172709 is about 276.6466886108.

It can be divided in two parts, 2 and 1172709, that added together give a palindrome (1172711).

The spelling of 21172709 in words is "twenty-one million, one hundred seventy-two thousand, seven hundred nine".