21505390 has 16 divisors (see below), whose sum is σ = 38882880. Its totient is φ = 8563680.

The previous prime is 21505381. The next prime is 21505417. The reversal of 21505390 is 9350512.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2406 + ... + 6985.

It is an arithmetic number, because the mean of its divisors is an integer number (2430180).

Almost surely, 2^21505390 is an apocalyptic number.

21505390 is a deficient number, since it is larger than the sum of its proper divisors (17377490).

21505390 is a wasteful number, since it uses less digits than its factorization.

21505390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9627.

The product of its (nonzero) digits is 1350, while the sum is 25.

The square root of 21505390 is about 4637.3904299724. The cubic root of 21505390 is about 278.0881231248.

The spelling of 21505390 in words is "twenty-one million, five hundred five thousand, three hundred ninety".