21425381 has 4 divisors (see below), whose sum is σ = 21434700. Its totient is φ = 21416064.

The previous prime is 21425377. The next prime is 21425387. The reversal of 21425381 is 18352412.

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 can be written as a sum of positive squares in 2 ways, for example, as 14508481 + 6916900 = 3809^2 + 2630^2 .

It is a cyclic number.

It is not a de Polignac number, because 21425381 - 2² = 21425377 is a prime.

It is a super-2 number, since 2×21425381² = 918093901990322, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21425381.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21425387) 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, 1535 + ... + 6723.

It is an arithmetic number, because the mean of its divisors is an integer number (5358675).

Almost surely, 2^21425381 is an apocalyptic number.

It is an amenable number.

21425381 is a deficient number, since it is larger than the sum of its proper divisors (9319).

21425381 is an equidigital number, since it uses as much as digits as its factorization.

21425381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9318.

The product of its digits is 1920, while the sum is 26.

The square root of 21425381 is about 4628.7558803635. The cubic root of 21425381 is about 277.7428267077.

Adding to 21425381 its reverse (18352412), we get a palindrome (39777793).

The spelling of 21425381 in words is "twenty-one million, four hundred twenty-five thousand, three hundred eighty-one".