21087905 has 32 divisors (see below), whose sum is σ = 28366848. Its totient is φ = 14976000.

The previous prime is 21087889. The next prime is 21087917. The reversal of 21087905 is 50978012.

It is not a de Polignac number, because 21087905 - 2⁴ = 21087889 is a prime.

It is a super-3 number, since 3×21087905³ (a number of 23 digits) contains 333 as substring.

It is a Smith number, since the sum of its digits (32) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 139580 + ... + 139730.

It is an arithmetic number, because the mean of its divisors is an integer number (886464).

Almost surely, 2^21087905 is an apocalyptic number.

It is an amenable number.

21087905 is a deficient number, since it is larger than the sum of its proper divisors (7278943).

21087905 is a wasteful number, since it uses less digits than its factorization.

21087905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 257.

The product of its (nonzero) digits is 5040, while the sum is 32.

The square root of 21087905 is about 4592.1569006296. The cubic root of 21087905 is about 276.2768392533.

The spelling of 21087905 in words is "twenty-one million, eighty-seven thousand, nine hundred five".