21519709 has 2 divisors, whose sum is σ = 21519710. Its totient is φ = 21519708.

The previous prime is 21519691. The next prime is 21519713. The reversal of 21519709 is 90791512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20448484 + 1071225 = 4522^2 + 1035^2 .

It is a cyclic number.

It is not a de Polignac number, because 21519709 - 2⁵ = 21519677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21519209) 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 as a sum of consecutive naturals, namely, 10759854 + 10759855.

It is an arithmetic number, because the mean of its divisors is an integer number (10759855).

Almost surely, 2^21519709 is an apocalyptic number.

It is an amenable number.

21519709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21519709 is an equidigital number, since it uses as much as digits as its factorization.

21519709 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5670, while the sum is 34.

The square root of 21519709 is about 4638.9340370391. The cubic root of 21519709 is about 278.1498295217.

The spelling of 21519709 in words is "twenty-one million, five hundred nineteen thousand, seven hundred nine".