21785491 has 16 divisors (see below), whose sum is σ = 27324864. Its totient is φ = 16907904.

The previous prime is 21785471. The next prime is 21785497. The reversal of 21785491 is 19458712.

It is not a de Polignac number, because 21785491 - 2¹⁷ = 21654419 is a prime.

It is a super-2 number, since 2×21785491² = 949215236222162, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21785491.

It is not an unprimeable number, because it can be changed into a prime (21785497) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2565 + ... + 7081.

It is an arithmetic number, because the mean of its divisors is an integer number (1707804).

Almost surely, 2^21785491 is an apocalyptic number.

21785491 is a deficient number, since it is larger than the sum of its proper divisors (5539373).

21785491 is a wasteful number, since it uses less digits than its factorization.

21785491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4590.

The product of its digits is 20160, while the sum is 37.

The square root of 21785491 is about 4667.4930101715. The cubic root of 21785491 is about 279.2902560326.

The spelling of 21785491 in words is "twenty-one million, seven hundred eighty-five thousand, four hundred ninety-one".