21272909 has 6 divisors (see below), whose sum is σ = 24746094. Its totient is φ = 18233880.

The previous prime is 21272843. The next prime is 21272947. The reversal of 21272909 is 90927212.

It can be written as a sum of positive squares in only one way, i.e., 11526025 + 9746884 = 3395^2 + 3122^2 .

It is not a de Polignac number, because 21272909 - 2²⁰ = 20224333 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21275909) 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 in 5 ways as a sum of consecutive naturals, for example, 217022 + ... + 217119.

It is an arithmetic number, because the mean of its divisors is an integer number (4124349).

Almost surely, 2^21272909 is an apocalyptic number.

It is an amenable number.

21272909 is a deficient number, since it is larger than the sum of its proper divisors (3473185).

21272909 is an equidigital number, since it uses as much as digits as its factorization.

21272909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 434155 (or 434148 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 32.

The square root of 21272909 is about 4612.2563892308. The cubic root of 21272909 is about 277.0824128009.

The spelling of 21272909 in words is "twenty-one million, two hundred seventy-two thousand, nine hundred nine".