21479209 has 2 divisors, whose sum is σ = 21479210. Its totient is φ = 21479208.

The previous prime is 21479191. The next prime is 21479221. The reversal of 21479209 is 90297412.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21187609 + 291600 = 4603^2 + 540^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21479209 is a prime.

It is a super-2 number, since 2×21479209² = 922712838531362, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21471209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10739604 + 10739605.

It is an arithmetic number, because the mean of its divisors is an integer number (10739605).

Almost surely, 2^21479209 is an apocalyptic number.

It is an amenable number.

21479209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21479209 is an equidigital number, since it uses as much as digits as its factorization.

21479209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 34.

The square root of 21479209 is about 4634.5667542932. The cubic root of 21479209 is about 277.9752276807.

The spelling of 21479209 in words is "twenty-one million, four hundred seventy-nine thousand, two hundred nine".