21478009 has 16 divisors (see below), whose sum is σ = 26219520. Its totient is φ = 17196480.

The previous prime is 21478007. The next prime is 21478049. The reversal of 21478009 is 90087412.

It is not a de Polignac number, because 21478009 - 2¹ = 21478007 is a prime.

It is a super-2 number, since 2×21478009² = 922609741208162, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21478007) 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, 4587 + ... + 7999.

It is an arithmetic number, because the mean of its divisors is an integer number (1638720).

Almost surely, 2^21478009 is an apocalyptic number.

21478009 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21478009 is a deficient number, since it is larger than the sum of its proper divisors (4741511).

21478009 is a wasteful number, since it uses less digits than its factorization.

21478009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3480.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21478009 is about 4634.4372905456. The cubic root of 21478009 is about 277.9700509462.

The spelling of 21478009 in words is "twenty-one million, four hundred seventy-eight thousand, nine".