21390381 has 12 divisors (see below), whose sum is σ = 30983680. Its totient is φ = 14220360.

The previous prime is 21390379. The next prime is 21390389. The reversal of 21390381 is 18309312.

It is not a de Polignac number, because 21390381 - 2¹ = 21390379 is a prime.

It is a super-2 number, since 2×21390381² = 915096798650322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390389) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 276 + ... + 6546.

Almost surely, 2^21390381 is an apocalyptic number.

It is an amenable number.

21390381 is a deficient number, since it is larger than the sum of its proper divisors (9593299).

21390381 is a wasteful number, since it uses less digits than its factorization.

21390381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6656 (or 6653 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21390381 is about 4624.9736215464. The cubic root of 21390381 is about 277.5915062236.

Adding to 21390381 its reverse (18309312), we get a palindrome (39699693).

The spelling of 21390381 in words is "twenty-one million, three hundred ninety thousand, three hundred eighty-one".