21320405 has 16 divisors (see below), whose sum is σ = 26817024. Its totient is φ = 16251840.

The previous prime is 21320401. The next prime is 21320407. The reversal of 21320405 is 50402312.

It is not a de Polignac number, because 21320405 - 2² = 21320401 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21320401) 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, 9359 + ... + 11411.

It is an arithmetic number, because the mean of its divisors is an integer number (1676064).

Almost surely, 2^21320405 is an apocalyptic number.

It is an amenable number.

21320405 is a deficient number, since it is larger than the sum of its proper divisors (5496619).

21320405 is a wasteful number, since it uses less digits than its factorization.

21320405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2156.

The product of its (nonzero) digits is 240, while the sum is 17.

The square root of 21320405 is about 4617.4024082811. The cubic root of 21320405 is about 277.2884733836.

Adding to 21320405 its reverse (50402312), we get a palindrome (71722717).

The spelling of 21320405 in words is "twenty-one million, three hundred twenty thousand, four hundred five".