21478391 has 16 divisors (see below), whose sum is σ = 24062208. Its totient is φ = 19008000.

The previous prime is 21478363. The next prime is 21478393. The reversal of 21478391 is 19387412.

It is a de Polignac number, because none of the positive numbers 2^k-21478391 is a prime.

It is a super-2 number, since 2×21478391² = 922642559897762, which contains 22 as substring.

It is a Smith number, since the sum of its digits (35) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21478393) 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, 111191 + ... + 111383.

It is an arithmetic number, because the mean of its divisors is an integer number (1503888).

Almost surely, 2^21478391 is an apocalyptic number.

21478391 is a deficient number, since it is larger than the sum of its proper divisors (2583817).

21478391 is a wasteful number, since it uses less digits than its factorization.

21478391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 422.

The product of its digits is 12096, while the sum is 35.

The square root of 21478391 is about 4634.4785035643. The cubic root of 21478391 is about 277.9716988942.

The spelling of 21478391 in words is "twenty-one million, four hundred seventy-eight thousand, three hundred ninety-one".