21505365 has 48 divisors (see below), whose sum is σ = 44487360. Its totient is φ = 9828000.

The previous prime is 21505349. The next prime is 21505381. The reversal of 21505365 is 56350512.

It is an interprime number because it is at equal distance from previous prime (21505349) and next prime (21505381).

It is not a de Polignac number, because 21505365 - 2⁴ = 21505349 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 4990 + ... + 8240.

It is an arithmetic number, because the mean of its divisors is an integer number (926820).

Almost surely, 2^21505365 is an apocalyptic number.

It is an amenable number.

21505365 is an abundant number, since it is smaller than the sum of its proper divisors (22981995).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21505365 is a wasteful number, since it uses less digits than its factorization.

21505365 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3279 (or 3266 counting only the distinct ones).

The product of its (nonzero) digits is 4500, while the sum is 27.

The square root of 21505365 is about 4637.3877344902. The cubic root of 21505365 is about 278.0880153657.

Adding to 21505365 its reverse (56350512), we get a palindrome (77855877).

The spelling of 21505365 in words is "twenty-one million, five hundred five thousand, three hundred sixty-five".