21509265 has 16 divisors (see below), whose sum is σ = 34771968. Its totient is φ = 11352576.

The previous prime is 21509261. The next prime is 21509269. The reversal of 21509265 is 56290512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21509261) and next prime (21509269).

It is not a de Polignac number, because 21509265 - 2² = 21509261 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21509261) 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, 5937 + ... + 8846.

It is an arithmetic number, because the mean of its divisors is an integer number (2173248).

Almost surely, 2^21509265 is an apocalyptic number.

It is an amenable number.

21509265 is a deficient number, since it is larger than the sum of its proper divisors (13262703).

21509265 is a wasteful number, since it uses less digits than its factorization.

21509265 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14888.

The product of its (nonzero) digits is 5400, while the sum is 30.

The square root of 21509265 is about 4637.8082107823. The cubic root of 21509265 is about 278.1048247790.

Adding to 21509265 its reverse (56290512), we get a palindrome (77799777).

The spelling of 21509265 in words is "twenty-one million, five hundred nine thousand, two hundred sixty-five".