21397609 has 2 divisors, whose sum is σ = 21397610. Its totient is φ = 21397608.

The previous prime is 21397603. The next prime is 21397631. The reversal of 21397609 is 90679312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16321600 + 5076009 = 4040^2 + 2253^2 .

It is a cyclic number.

It is not a de Polignac number, because 21397609 - 2³ = 21397601 is a prime.

It is not a weakly prime, because it can be changed into another prime (21397601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10698804 + 10698805.

It is an arithmetic number, because the mean of its divisors is an integer number (10698805).

Almost surely, 2^21397609 is an apocalyptic number.

It is an amenable number.

21397609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21397609 is an equidigital number, since it uses as much as digits as its factorization.

21397609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20412, while the sum is 37.

The square root of 21397609 is about 4625.7549654083. The cubic root of 21397609 is about 277.6227695821.

The spelling of 21397609 in words is "twenty-one million, three hundred ninety-seven thousand, six hundred nine".