21423009 has 16 divisors (see below), whose sum is σ = 30551040. Its totient is φ = 13305600.

The previous prime is 21423007. The next prime is 21423019. The reversal of 21423009 is 90032412.

It is not a de Polignac number, because 21423009 - 2¹ = 21423007 is a prime.

It is a super-2 number, since 2×21423009² = 917890629228162, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21423007) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3072 + ... + 7230.

It is an arithmetic number, because the mean of its divisors is an integer number (1909440).

Almost surely, 2^21423009 is an apocalyptic number.

It is an amenable number.

21423009 is a deficient number, since it is larger than the sum of its proper divisors (9128031).

21423009 is a wasteful number, since it uses less digits than its factorization.

21423009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4280.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21423009 is about 4628.4996489143. The cubic root of 21423009 is about 277.7325767103.

It can be divided in two parts, 2142 and 3009, that added together give a triangular number (5151 = T₁₀₁).

The spelling of 21423009 in words is "twenty-one million, four hundred twenty-three thousand, nine".