21505385 has 32 divisors (see below), whose sum is σ = 29635200. Its totient is φ = 14837760.

The previous prime is 21505381. The next prime is 21505417. The reversal of 21505385 is 58350512.

It is not a de Polignac number, because 21505385 - 2² = 21505381 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21505381) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 154646 + ... + 154784.

It is an arithmetic number, because the mean of its divisors is an integer number (926100).

Almost surely, 2^21505385 is an apocalyptic number.

It is an amenable number.

21505385 is a deficient number, since it is larger than the sum of its proper divisors (8129815).

21505385 is a wasteful number, since it uses less digits than its factorization.

21505385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281.

The product of its (nonzero) digits is 6000, while the sum is 29.

The square root of 21505385 is about 4637.3898908761. The cubic root of 21505385 is about 278.0881015730.

Adding to 21505385 its reverse (58350512), we get a palindrome (79855897).

The spelling of 21505385 in words is "twenty-one million, five hundred five thousand, three hundred eighty-five".