21778231 has 4 divisors (see below), whose sum is σ = 21789000. Its totient is φ = 21767464.

The previous prime is 21778223. The next prime is 21778259. The reversal of 21778231 is 13287712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21778231 - 2³ = 21778223 is a prime.

It is a super-2 number, since 2×21778231² = 948582690978722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21778193 and 21778202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21778201) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1336 + ... + 6733.

It is an arithmetic number, because the mean of its divisors is an integer number (5447250).

Almost surely, 2^21778231 is an apocalyptic number.

21778231 is a deficient number, since it is larger than the sum of its proper divisors (10769).

21778231 is an equidigital number, since it uses as much as digits as its factorization.

21778231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10768.

The product of its digits is 4704, while the sum is 31.

The square root of 21778231 is about 4666.7152259378. The cubic root of 21778231 is about 279.2592281566.

The spelling of 21778231 in words is "twenty-one million, seven hundred seventy-eight thousand, two hundred thirty-one".