21291305 has 32 divisors (see below), whose sum is σ = 31138560. Its totient is φ = 13651200.

The previous prime is 21291301. The next prime is 21291311. The reversal of 21291305 is 50319212.

It is not a de Polignac number, because 21291305 - 2² = 21291301 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21291301) 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, 67007 + ... + 67323.

It is an arithmetic number, because the mean of its divisors is an integer number (973080).

Almost surely, 2^21291305 is an apocalyptic number.

It is an amenable number.

21291305 is a deficient number, since it is larger than the sum of its proper divisors (9847255).

21291305 is a wasteful number, since it uses less digits than its factorization.

21291305 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 449.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21291305 is about 4614.2502099474. The cubic root of 21291305 is about 277.1622598884.

The spelling of 21291305 in words is "twenty-one million, two hundred ninety-one thousand, three hundred five".